Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

Abstract

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR₄) or inorganic adamantane-type compounds of the general formula [(RT)₄E₆] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH₂) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) – depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH₂Sn(E)R′}₃], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such ‘cluster glasses’ form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

Adamantane-type clusters exhibit a huge diversity of chemical compositions, structural details, and resulting properties.

1. Introduction

Diamond, in its cubic modification, is the hardest solid on Earth, which is due to the unique structure and bonding with four strong bonds directing in a perfectly tetrahedral manner to four neighbors in a three-dimensional network of face-centered cubic (F3̄m) symmetry.¹ It is therefore reasonable that the heavier congeners, Si, Ge, and α-Sn also adopt this structure. However, not only those, but also isoelectronic binary or multinary solids follow this structural concept, as the same overall electron count allows for a corresponding electronic structure of the material. The most well-known examples are 1 : 1 combinations of atoms of groups 13 and 15 or 12 and 16 such as GaAs or ZnS, but more complex compositions, like CuFeS₂, can also be derived from the cubic diamond network by replacement of the atomic sites in a tetragonal superstructure. Moreover, there are also “filled” versions, like the Zintl phase NaTl with two intertwining diamond networks of covalently bonded Tl atoms and non-bonding Na⁺ cations, or crystobalite-type SiO₂ with O atoms bridging between the Si atoms that are arranged in a diamond-type pattern. Naturally, the chemical and physical properties of the materials vary as a consequence of the different elemental combinations and corresponding changes in bond strengths and electronic structures. This is extensively taken advantage of in technical applications – starting with the electrical insulator and heat conductor diamond, via all kinds of semiconductor applications of the heavier homologues and the binary analogs, to more specific applications of the more complex compounds.

However, the structure and bonding concept of diamond, which is overwhelmingly successful in solid state compounds, is not restricted to the three-dimensional extension. On the contrary, molecular fragments of these structures are even more diverse. The parent structural fragment of diamond is adamantane (derived from the greek adamas for diamond). The adamantane-type topology (or adamantane-type scaffold) is based on a core structure with ten atoms, four of which represent the bridgehead atoms, and six of which occupy the briding positions. It has a sum formula of C₁₀H₁₆ (or (CH)₄(CH₂)₆) and was first proposed in 1924 by Decker, who investigated the compound under the name “decaterpene,” which would later be recognized as adamantane.² However, due to its exceedingly low natural abundance (0.0004%),³ it took another decade until adamantane was identified in crude oil in Hodonin, Czechoslovakia in 1933. The adamantane-type scaffold, just like its parent solid state structures, is found in a multitude of compounds scattered throughout the periodic table. Innumerous admantane derivatives have been realized – either by replacing H with other atoms or molecules, or by isoelectronic replacement of some or all of the C atoms or CH₂ units – like in the related solids with diamond-type structures. A very prominent derivative of the admantane molecule is urotropine, N₄(CH₂)₆, a condensation product of ammonia and formaldehyde, in which the C–H bridgehead units are replaced with isoelectronic N atoms. There are also purely inorganic analogs. One of the first purely inorganic adamantane-type molecules, and maybe the most prominent example, is phosphorous pentaoxide that consists of binary molecules of P₄O₁₀, the structure of which was suggested in the late 19th century.⁴ Inorganic cluster cores of the type {Q₄E₆} are obtained when replacing the bridgehead C atoms (position Q) with atoms of another group 14 element and the CH₂ groups (position E) with atoms of a group 16 element. Saturation of the bridgehead atoms requires a substituent to form either binary anions [Q₄E₁₀]⁴⁻ (Q = Si, Ge, Sn) or hybrid clusters of the type [(RQ)₄E₆], with Q = group 14 element Si, Ge, or Sn and R = organic or organometallic group substituent.

While the first observation of these molecules was unintended and caused excitement for the beautiful structure, the development is now in the direction of the compounds' intriguing chemical and physical properties. With regard to the effects of the substitution of elements on these features, the same rules apply to molecules as to solids, which enables fine-tuning across a broad spectrum. To make use of these properties, however, it is necessary to know all about the synthetic approaches and their respective modifications, and develop them further. In this review, we therefore aim at giving a comprehensive overview of the various synthesis pathways of compounds with a molecular adamantane-type structure across the periodic table, and discuss methods for the functionalization of the organic adamantane. To keep in scope, we have decided to limit the organic synthesis to tetrasubstituted adamantanes. Based on this, we will further elaborate on the optical (nonlinear) properties and structural features of the different compounds in the solid state.

2. Variety of compositions and syntheses

2.1. Inorganic and hybrid compounds

Inorganic and hybrid compounds featuring adamantane-type architectures are formed with elements from nearly all groups across the periodic table. In this section, we will discuss their synthetic access and elaborate on prevalent methods for the formation of molecules with specific elemental combinations. This will be discussed for each combination of groups from the periodic table using the Q/E nomenclature introduced above, with Q representing the atom(s) featuring three bonds within the adamantane-type structure, and E representing the atoms or groups bridging between two of the former positions. Some methods are commonly used for all elements and will be briefly discussed first with one example given for each; for easier tracking, a letter will be assigned to those procedures, to be referred to later in the course of this article.

Method A

One common synthesis method is a solid-state reaction starting directly from the elements or from binary salts. It is a simple way to realize uncomplicated adamantane molecules, but it also requires high temperatures, which prohibits the use of some precursors (Scheme 1, top left).

Scheme 1. Simplified representation of the synthetic Methods A–N for the formation of adamantane-type clusters.

Example:²⁵³

Method B

Similar to Method A, solvothermal reactions are commonly used to generate adamantane-like structures. In those reactions, a solvent, elements or binary precursors (as well as some additives, if applicable) are reacted in a closed vessel at elevated temperatures. Compared to Method A, these oftentimes use lower temperatures, and milder conditions allow for the use of more diverse precursors (Scheme 1, top left).

Example:⁶⁵

Method C

As in A or B, simple salts or elements are reacted, but this time, the reaction takes place in solution at temperatures below their respective boiling points in open vessels. The very mild conditions allow for the addition of additives or catalysts and for more thermally unstable adamantanes to be realized (Scheme 1, top left).

Example:²⁵³

Method D

If the precursor used for the Q component contains three leaving groups and those for E contain two, a condensation reaction can yield adamantane compounds with each bond of the scaffold formally formed by one condensation event. This mostly occurs for metal (pseudo)halides reacted with alkaline metal salts of E anions, H_xE, or silyl derivatives of E. Such syntheses are normally carried out in solution at mild temperatures. The formation of the condensation side product can be the driving force in the reaction (Scheme 1, left upper center).

Example:³⁰⁴

Method E

Some purely inorganic molecules can be obtained by first creating a solid phase—by melting the corresponding elements or binary salts—and subsequently extracting this phase with an appropriate solvent. This sometimes takes place in the presence of a sequestering agent, like a crown ether or a cryptand, or other additives. Common solvents for this method are ethane-1,2-diamine or THF (Scheme 1, left lower center).

Example:²⁸²

Method F

Gaseous reactants like H₂S, H₂, O₂ or PH₃ can be introduced to solid reaction partners at high temperatures to occupy the E position during construction of the adamantane scaffold (Scheme 1, bottom left).

Example:³⁰⁴

Method G

Similar to F, but in the liquid phase, hence these reactions often do not require high temperatures (Scheme 1, bottom left).

Example:^78,79

Method H

Thermal decomposition of a precursor can lead to the formation of simple adamantanes, sometimes in the presence of a catalyst or additive (Scheme 1, top right).

Example:^62,63

Method I

Chemically induced decomposition by hydrolysis or acidic decomposition of a precursor can afford adamantane-type clusters, especially for oxide and hydroxide species. From a mechanistic viewpoint, this is often similar to Method D, but may happen unintentionally under ambient conditions (Scheme 1, top right).

Example:¹¹⁶

Method J

In some cases, rearrangement of molecules or other cluster architectures to the adamantane-type scaffold induced by heat, catalysts, or other reactants were reported (Scheme 1, right upper center).

Example:²⁸

Method K

Multidentate organic ligands, mostly with oxygen or nitrogen sites, or preformed cluster fragments can be used as templates to fill the E position in adamantane-type compounds (Scheme 1, right lower center).

Example:³⁰

Method L

Reactions towards adamantane-type clusters can be induced by sonication (Scheme 1, bottom right).

Example:²⁹

Method M

Mechanochemical reactions can prompt isomerisation to the desired adamantane-type molecules (Scheme 1, bottom right).

Example:⁸⁶

Method N

Electrochemical methods can form adamantane-type clusters from appropriate electrodes and electrolytes (Scheme 1, bottom right).

Example:¹⁹⁴

Method O

For ionic clusters, new compounds can be generated by exchanging the counter ion to introduce new functionalities or templating counter ions (Scheme 2, top).

Scheme 2. Simplified representation of the synthetic Methods O–S for the formation of adamantane-type clusters by modification of an adamantane-type cluster compound.

Example:²⁹³

Method P

In a few cases, ligands can be added to an existing adamantane core in a position that did not previously form bonds outside the cluster scaffold (Scheme 2, top left).

Example:^345–347

Method Q

Clusters with (organic) ligands can be expanded by modification of the ligand, by formal ligand exchange, or by ligand abstraction to afford new compounds (Scheme 2, top right).

Example:⁵¹²

Method R

Reactions of adamantane-type or other clusters to replace atoms in their inorganic core, sometimes combined with a rearrangement of the architecture to the adamantane scaffold. This includes exchange reactions in Q and E positions between adamantanes. This method can also be used to create larger clusters with ternary inorganic cores of other architectures, especially when an anion source is additionally provided (Scheme 2, bottom left).

Example:¹³¹

Method S

Chemical reduction or oxidation of an adamantane-type cluster can, in some cases, be done under retainment of its structural motif (Scheme 2, bottom right).

Example:¹³¹

Method T

A method for the generation of extended structures is the linkage of inorganic adamantane-type clusters using transition metal compounds or other linkers in solution. Sometimes, this is combined with an ion exchange and some additives (Scheme 3).

Scheme 3. Simplified representation of the synthetic Method T to generate a polymeric compound from adamantane-type clusters.

Example:⁵³³

Method U

There are a couple of unique approaches, which are not outlined in this overview.

In the following, we will dicuss all different families of adamantane-type compounds in groups sorted by their elemental combination. This will be done in order of the group of the atoms in the E position, starting with hydride clusters and moving along to halide species. The only main groups that do not occur in the E position are groups 2 and 18.

Being rather uncommon, examples with transition metal atoms in the Q positions will be discussed last. In some of the final subsection, we will give an overview of clusters comprising elements from different groups in their scaffold, as well as extended and polymeric species.

All cluster examples, along with their simplified synthesis/reaction methods, are given in tables at the end of each section (Tables 1–23); for the sake of readability, the respective synthesis methods are not always referred to in the main text though. If the reaction temperature is not specified in the table, the reaction was carried out at ambient temperature. Similarly, reactions without specified durations occur instantaneously. Purification times and methods are not included for purifications that occur in additional, subsequent steps.

Adamantane-type compounds with hydrogen or group 1 atoms in the E position^a.

Compound	Reagents/conditions	Method
[(MgIDipp)2(MgHMDS)2H6] (1)	IDipp, [Mg{N(SiMe3)2}2], PhSiH3/hexane, 60 °C, 3 h	C11
[(CaTACNMe)4H6][B(C6H3-3,5-Me2)] (2)	H2 (1 bar), [(Me3TACNMe)Ca(CH2Ph)(thf)x][B(C6H3-3,5-Me2)]/THF, 70 °C, 6 h	G12
[AsPh4]2[Re4(CO)12H6] (3)	Re2(CO)10, NaBH4, (C6H5)4AsCl/THF, EtOH	C13
[Me3BnN]2[Re4(CO)12H6] (4)	Re2(CO)10, KOH, [Me3BnN]Cl/MeOH, 65 °C, prolonged heating	H14
[(Cp*Zr)4H6] (5)	[(μ-H)(μ3-H)(Cp*ZrCl)]4, Na in Hg/Et2O, 1 month	J5
[(ZnIDipp)2(ZnHMDS)2H6] (6)	Zn(HMDS)2, IDipp, DMAB/cyclohexane, RT, 30 min	C15
[Ir4(IMe)7(CO)H10][BF4]2 (7)	[Ir(cod)(IMe)2][BF4], KOH, Na[BarF]/glycerol, H2O, 120 °C, 24 h	J16
[Ir4(IMe)7(CO)H10][BArF]2 (8)	[Ir4(IMe)7(CO)H10][BF4]2 (7), Na[BarF]/dichlormethane, 2 h	O16
[Ir4(IMe)8H10][BArF]2 (9)	[Ir(cod)(IMe)2] [BF4], KOH, NaBarF/glycerol, H2O, 120 °C, 24 h	J17
[{Me2P(BH3)CHSiMe2OLi}4Li4(Et2O)2.75(thf)1.25] (10)	1. Me3P(BH3), n-BuLi/THF, 2 h	J18
	2. (Me2SiO)3/Et2O, 2 h

^aIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, HMDS = 1,1,1,3,3,3-hexamethyldisilazide, TACNMe = 1,4,7-trimethyl-1,4,7-triazacyclononane, Bn = benzyl, Cp* = pentamethylcyclopentadienyl, DMAP = dimethylamine borane, BAr^F = [B[3,5-(CF₃)₂C₆H₃].

Adamantane-type compounds with group 13 atoms in the E position^a.

Compound	Reagents/conditions	Method
[(CH)4(BMe)6] (11)	BMe3/450 °C, 40 min	H19,20
[(CH)4(BCl)6] (12)	(Cl2B)2CH2/450 °C to RT, 12 h	H21
[(CH)4(BEt)6] (13)	HC(BEt2)3, BEt2, AlEt3/150 °C	A22
[(CMe)4(BEt)6] (14)	(BEt)3(CMe)2, I2, K/THF	J23
[(EtC)4(GaEt)6] (15)	Et2GaH, HC≡CEt/−196 °C to RT, 4 h	U24
[(nBuC)4(GaEt)6] (16)	Et2GaH, HC≡CnBu/4 h	U24
[(EtC)4(GaMe)6] (17)	Me2GaH, HC≡CEt/−196 °C to RT, 4 h	U24
[Li(thf)4]2[(tBuAs)4(GaCl2)6] (18)	Li2AstBu, GaCl3/Et2O, −78 °C to RT, 3 days	C25
Li2[(RN)4(AlH2)6] (19–20, R = Me, tBu)	Li[AlH4], [RNH3]Cl,/Et2O, 4 weeks	C26
Na2[S4(BH2)6] (21)	THF·BH3, Na[BH4], H2S/0 °C	C27
Na2[Se4(BH2)6] (22)	1. Se, Na[BH4]/diglyme, 0 °C to 110 °C, 8 h	B27
	2. THF·BH3/diglyme
Cs2[S4(BH2)6] (23)	Na2[S4(BH2)6] (21), CsBr/H2O	O27
Cs2[Se4(BH2)6] (24)	Na2[Se4(BH2)6] (22), CsBr/H2O	O27
DMPyr2[S4(InMe2)6] (25)	DMPyr3[Me2In(SInMe3)]3/THF, pentane, 14 days	J28
[Ga(C6H5Me)2]2[{AgGa(OTf)3}4Ga6(OTf)4] (26)	AgOTf, Ga/toluene, 45 °C, 1.5 h (ultrasonic activation)	L29

^{a n} Bu = normal butyl, ^tBu = tertiary butyl, diglyme = bis(2-methoxyethyl) ether, DMPyr = 1,1-dimethylpyrrolidinium, OTf = O₃SCF₃

Adamantane-type compounds with group 2 and transition metals in the Q position and group 14 atoms in E position^a.

Compound	Reagents/conditions	Method
[(μ4-O)Ca4(2,6-dimethoxyphenyl)6] (27)	(2,6-Dimethoxyphenyl)K, CaI2/THF, 3 days	K30
[Fe4(Ph)6(THF)4] (28)	Fe(acac)3, PhMgBr/THF, −30 °C, 25 min	C31
[Fe4(p-tolyl)6(THF)4] (29)	Fe(acac)3, p-tolylMgBr/THF, −30 °C, 25 min	C31
[Fe4(p-tolyl)6(THF)3] (30)	Fe(acac)3, p-tolylMgBr/THF, −30 °C, 25 min	C31
[Fe4(4-F-Ph)6(THF)4] (31)	Fe(acac)3, 4-F-PhMgBr/THF, −30 °C, 25 min	C31
[BMIm]2[{Fe(CO)3}4Sn6I10] (32)	SnI4, Fe(CO)5, [BMIm][NTf2]/130 °C, 4 days	B32
[BMIm]6[S][{Fe(CO)3}4Sn6I10]2 (33)	SnI4, NH4I, Fe(CO)5, [BMIm][OTf]/130 °C, 4 days	B32
[{NiP(CH2CH2CN)3}4(CO)6] (34)	Tris-(2-cyanoethyl)phosphine, Ni(CO)4/MeOH, 70 °C, 24 h	B33
[(NiPMe3)4}[BF4][(NiPMe3)4(CO)6] (35)	Ni(COMe)Cl(PMe3)2, PMe3, Tl[BF4]/CH2Cl2, RT, 30 min	C34
[(NiPMe3)4(CO)6] (36)	Bis(cod)nickel, PMe3, CO/toluene, RT, 6 h	F35
[(NiPnBu3)4(CO)6] (37)	Bis(cod)nickel, PnBu3, CO/toluene, RT, 6 h	F35
[(PdPnBu3)4(CO)6] (38)	Pd4(CO)5(PBu3n)4, CH3COOH/EtOH, pentane, RT, 2 days or Pd(OAc)2, CH3COOH, CO, PBu3n/dioxane, Me2CO, 5 days	J/F36

^acod = 1,5-cyclooctadiene, OAc = acetate, acac = acetylacetonate, BMIm = 1-butyl-3-methyl-imidazolium, NTf₂ = bistrifluoridomethansulfonimide.

Adamantane-type compounds with group 14 elements in the Q position and group 14 atoms in the E position^a.

Compound	Reagents/conditions	Method
[(SiCl)4(CH2)6] (39)	SiCl4, Me3SiCl, AlCl3/500 °C or [(SiMe)4(CH2)6], Cl2, I2/CCl4	B/Q37,39,42
[(SiMe)4(CH2)6] (40)	SiMe4/700 °C or (Me2SiCH2)3, AlBr3/100 °C	A38,40,41
[(SiH)4(CH2)6] (41)	Li[AlH4], [(SiMe)4(CH2)6] (40)	Q39
[(SiMe)3SiBr(CH2)6] (42)	(Me2SiCH2)3, AlBr3/100 °C	J41,43
[(SiMe)2(SiBr)2(CH2)6] (43)	(Me2SiCH2)3, AlBr3/100 °C	J41
[(SiMe)3SiCl(CH2)6] (44)	(Me2SiCH2)3, AlCl3/100 °C	J41
[(SiMe)2(SiCl)2(CH2)6] (45)	(Me2SiCH2)3, AlCl3/100 °C	J41
[SiMe(SiCl)3(CH2)6] (46)	[(SiMe)4(CH2)6] (40), Cl2, I2/CCl4	Q42
[(SiMe)3SiOH(CH2)6] (47)	[(SiMe)3SiCl(CH2)6] (44), [NBu4]Cl, KOH/2-methyl-2-butanol, H2O, 80 °C, 30 min	Q44
[(SiMe)3SiOCH2CH2NMe2(CH2)6] (48)	[(SiMe)3SiCl(CH2)6] (44), HOCH2CH2NMe2, n-BuLi/hexane, 69 °C, 9 h	Q44
[(SiMe)3SiH(CH2)6] (49)	[(SiMe)3SiBr(CH2)6] (42), Li[AlH4]/Et2O, 35 °C, 4 days	Q44
[(SiMe)3SiNEt2(CH2)6] (50)	[(SiMe)3SiCl(CH2)6] (44), LiNEt2/hexane, 24 h	Q44
[(SiMe)3SiPh(CH2)6] (51)	[(SiMe)3SiCl(CH2)6] (44), LiPh/Et2O	Q45
[(SiMe)3SiOMe(CH2)6] (52)	[(SiMe)3SiBr(CH2)6] (42), NaOMe,/MeOH	Q45
[(SiMe)3SiF(CH2)6] (53)	[(SiMe)3SiBr(CH2)6] (42), c-C6H11NH3F,/CHCl3	Q45
[(SiMe)3SiOTf(CH2)6] (54)	[(SiMe)4(CH2)6] (40), ICl, AgOTf/CH2Cl2, 1 day	Q46
[(SiOTf)2(SiMe)2(CH2)6] (55)	[(SiMe)3SiOTf(CH2)6] (54), ICl, AgOTf/CH2Cl2, 24 h	Q46
[(SiMe)4(CH2)5CHSiMe2Ph] (56)	[(SiMe)4(CH2)6] (40), ClSiMe2Ph, n-BuLi, KOCMe3/THF, 0 °C, 10 h	Q47
[(SiMe)4(CH2)5CHSiMe2CH2SiMe2Ph] (57)	[(SiMe)4(CH2)5CHSiMe2Ph] (56), Br2, LiCH2SiMe2Ph/	Q47
[(SiMe)4(CH2)5CHSiMe2CH2SiMe2CH2SiMe3] (58)	[(SiMe)4(CH2)6] (40), Me3SiCH2SiMe2CH2SiMe2Br, n-BuLi, TMEDA/hexane, 40 °C, 5 h	Q47
[(SiMe)3(CH2)5CH(SiMe2CH2SiMe2CH2)Si] (59)	[(SiMe)4(CH2)5CHSiMe2CH2SiMe2CH2SiMe3] (59), AlBr3/30 °C, 20 h	Q47
[(SiBr)(SiMe)2(CH2)5CH(SiMe2CH2SiMe2CH2)Si] (60)	[(SiMe)4(CH2)5CHSiMe2CH2SiMe2CH2SiMe3] (59), AlBr3/30 °C, 20 h	Q47
[(SiMe)3Si(CH2)6][CHB11Cl11] (61)	[Ph3C][CHB11Cl11], [(SiMe)3SiH(CH2)6] (49)/PhBr	Q48
[(SiSiMe3)4(SiMe2)6] (62)	Si14Me24, [CPh3][B(C6F5)4]/Toluene, 48 h	J49,50
[(SiSiMe3)4(SiMe2)5(SiMeCl)] (63)	Si14Me24, AlCl3, MeI, Me3SiCl/C6H6, 48 h	J50
[(SiSiMe3)4(SiMe2)5(SiMeBr)] (64)	Si14Me24, AlBr3, MeI, Me3SiBr/C6H6, 17 days	J50
[(SiSiMe2Cl)(SiSiMe3)3(SiMe2)6] (65)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Me2SiCl2/1 h
[(SiSiMe2Ph)(SiSiMe3)3(SiMe2)6] (66)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Me2PhSiCl/3 h
[(SiSiPh3)(SiSiMe3)3(SiMe2)6] (67)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Ph3SiCl/3 h
[(SiSnMe3)(SiSiMe3)3(SiMe2)6] (68)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Me3SnCl/3 h
[(SiGeMe3)(SiSiMe3)3(SiMe2)6] (69)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Me3GeCl/3 h
[(SiH)(SiSiMe3)3(SiMe2)6] (70)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. HCl/3 h
[{SiP(NET2)2}(SiSiMe3)3(SiMe2)6] (71)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. P(NET2)2Cl/3 h
[(SiCH2SMe)(SiSiMe3)3(SiMe2)6] (72)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. ClCH2SMe/3 h
[(SiMe)(SiSiMe3)3(SiMe2)6] (73)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. Methyl-p-toluenesulfonate/3 h
[(SiBr)(SiSiMe3)3(SiMe2)6] (74)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. 1,2-Dibromoethane/3 h
[(SiCl)(SiSiMe3)3(SiMe2)6] (75)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. PCl3/−78 °C, 3 h
[(SiCH2SMe)2(SiSiMe3)2(SiMe2)6] (76)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. ClCH2SMe/3 h
[(SiCH2SMe)3(SiSiMe3)(SiMe2)6] (77)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. ClCH2SMe/3 h
[(SiCH2SMe)4(SiMe2)6] (78)	1. [(SiSiMe3)4(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. ClCH2SMe/3 h
[(SiMe)(SiiPr)(SiSiMe3)2(SiMe2)6] (79)	1. [(SiMe)(SiSiMe3)3(SiMe2)6] (62), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2.Chlorotriisopropylsilane/3 h
[(SiMe)(SiiPr)(SiCH2SMe) (SiSiMe3)(SiMe2)6] (80)	1. [(SiMe)(SiiPr)(SiSiMe3)2(SiMe2)6] (79), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2.ClCH2SMe/3 h
[(SiMe)(SiiPr)(SiCH2SMe)(SiBr)(SiMe2)6] (81)	1. [(SiMe)(SiiPr)(SiCH2SMe) (SiSiMe3)(SiMe2)6] (80), KOCMe3, 18-crown-6/toluene, 16 h	Q50
	2. 1,2-Dibromoethane/3 h
[(SiSiCl3)4(GeMe2)4(SiCl2)2] (82)	Me2GeCl2, Si2Cl6, [Bu4N]Cl/CH2Cl2, 13 days	C51
[(SiSiCl3)4(GeMe2)5(SiCl)] (83)	Me2GeCl2, Si2Cl6, [Bu4N]Cl/CH2Cl2, 19 days	C51
[(SiSiCl3)4(GeMe2)6] (84)	Me2GeCl2, Si2Cl6, [Bu4N]Cl/CH2Cl2, 60 °C, 6 days	C51
[(SiSiMe3)4(GeMe2)6] (85)	[(SiSiCl3)4(GeMe2)6] (85), MeMgBr/Et2O, 60 °C, 1 day	Q52
[(SiSiMe3)4(GeMe2)4(GeMe2)2] (86)	[(SiSiCl3)4(GeMe2)4(GeMe2)2] (86), MeMgBr/Et2O, 60 °C, 1 day	Q52
[(SiSiMe3)4(GeMe2)5(GeMe2)] (87)	[(SiSiCl3)4(GeMe2)5(GeMe2)] (87), MeMgBr/THF, Et2O, 1 day	Q52
[(SiSiCl3)4(SnMe2)4(SiCl2)2] (88)	Me2SnCl2, Si2Cl6, [Bu4N]Cl/CH2Cl2, 3 days	Q52
[(SiSiCl3)4(SnMe2)5(SiCl2)] (89)	[(SiSiCl3)4(SnMe2)4(SiCl2)2] (88), [Bu4N]Cl/CH2Cl2, 60 °C, 1 day	Q52

^aTMEDA = tetramethylethylenediamine, ⁱPr = isopropyl.

Adamantane-type compounds with group 15 elements in the Q position and group 14 atoms in the E position^a.

Compound	Reagents/conditions	Method
[P4(SiR2)6] (90–95, R2 = Me2, MeEt, Et2, MePh, (Me)(C2H3), MeH)	1. P4, K, Na,/DME, −78 °C	D53–56
	2. Cl2SiR2/DME, 24 h
[P4(SiMe2)6−x(SiEt2)x] (90, 96–100, 92, x = 0–6)	(Me3Si)2P–SiEt2Cl/300 °C	H57
[P4(SiMe2)6−x(SiMeEt)x] (90, 101–105, 91, x = 0–6)	(Me3Si)2P–SiMeEtCl/300 °C	H57
[P4(GeMe2)6] (106)	Me2Ge(PH2)2, Hg/100 °C, 24 h	H58,59
[P4(SnR2)6] (107–109, R = Me, nBu, Ph)	R2SnCl2, PH3/or P(SnMe3)3, [(ZnCl)2Fe(CO)4(thf)2]/THF, 4 days	D/J60,61
[As4(SiMe2)6] (110)	Me2Si(AsSiMe3)2/240 °C, 48 h	H62,63

^aDME = 1,2-dimethoxyethane.

Adamantane-type compounds with group 15 atoms in E position^a.

Compound	Reagents/conditions	Method
(Ph4P)2[(BeCl)4(N3)6] (111)	Me3SiN3, (Ph4P)2[Be2Cl6]/CH2Cl2, 2 days	C64
(Ph4P)2[(Be4Br)4(N3)6] (112)	Me3SiN3, (Ph4P)2[Be2Br6]/CH2Br2, 2 days	C64
[(BeNH3)4(NH2)6]Cl2 (113)	BeCl2, Be/NH3, 2 days	B65
[(BeNH3)4(NH2)6]Br2 (114)	BeBr2, Be/NH3, 2 days	B65
[(BeNH3)4(NH2)6]I2 (115)	NH4I, Be/NH3, 29 days	B65
[(BeNH3)4(NH2)6](CN)2 (116)	Me3SiCN, Be/NH3, 2 days	B65
[(BeNH3)4(NH2)6](SCN)2 (117)	NH4SCN, Be/NH3, 4 days	B65
[(BeNH3)4(NH2)6](N3)2 (118)	Me3SiN3, Be/NH3, 4 days	B65
[Li(thf)4]2[(CdPPh2)4(PPh2)6] (119)	n BuLi, Ph2PH, [Cd{N(SiMe3)2}2]/THF, 80 °C to RT, 12 h	C66
[Li(thf)4]2[Cu4(PPh2)6] (120)	n BuLi, Ph2PH, CuCN/toluene, −78 °C	C67
[Fe4(PiPr2)6] (121)	[FeBr2(thf)2], iPr2PLi/DME, RT	C68
[Fe4(N CPh2)6] (122)	FeBr2, LiN CPh2, Zn/THF, −25 °C to RT, 18 h	C69
[(AlCl)4(NMe2)4(NMe)2] (123)	(NMe2)2AlCl, B2(NMe2)4/240 °C, 10 h	B70,71
[Li(OEt2)3][(HAl)4(NPh)6{Li(OEt2)}3] (124)	PhN(H)Li, H3Al·N(Me)C5H8/Et2O	D72
[(ArMe6Al)4(PH2)4(PH)2] (125)	(ArMe6AlH2)2, PH3/toluene, 80 psi, 24 h	G73
[(PhGa)4(NHiBu)4(NiBu)2] (126)	[PhGa(NMe2)2]2, H2NiBu/2 h	C74
[(PhSi)4(PPh)6] (127)	PhSiCl3, K2PPh/C6H6, Et2O, DME, 10 h	D75
[(PhGe)4(PPh)6] (128)	PhGeCl3, K2PPh/C6H6, Et2O, DME, 10 h	D75
[(iPrSi)4(PH)6] (129)	Li[Al(PH2)4], iPrSiCl3/1,2-DME, −30 °C, 3 h	C76
[(C6H4{P(SitBuP)1,2})3(SitBu)] (130)	[Li(tmeda)]2[C6H4(PSiMe3)2-1,2], SitBuCl3/THF, −78 °C	J77
[P4(NMe)6] (131)	MeNH2, PCl3/−78 °C to RT, 4 days	G78,79
[P4(NEt)6] (132)	PCl3, EtNH2/−60 °C to 150 °C	G80,81
[P4(NBn)6] (133)	PCl3, nBuLi, BnNH2 NEt3/THF, −60 °C to RT, 5 days	D81
[As4(NMe)6] (134)	AsCl3, MeNH2/C6H6, 0 °C, 1 h	G82,83
[As4(NiPr)6] (135)	AsCl3, iPrNH2/pentane, 1 h	D82
[As4(NnBu)6] (136)	AsCl3, nBuNH2/C6H6, 60 °C, 30 min	D82
[P4(NiPr)6] (137)	1. ClP(NiPr)2PNiPrSiMe3/MeCN, 82 °C, 15 h	K84,85
	2. 158 °C, 3 days
[P4(NtBu)6] (138)	[P4(NtBu)6] (double decker isomer), LiCl/ball milling, 90 min	M86
[P3(PMe)(NMe)6Me]I (139)	[P4(NMe)6] (131), MeI/0 °C	P78,79,87
[(SP)4(NEt)6] (140)	[P4(NEt)6] (132), S/toluene, 95 °C, 9 h	P80
[(OP)4(NMe)6] (141)	[P4(NMe)6] (131), Me3NO/C6H6, 12 h	P90,91
[Pn(SP)4−n(NMe)6] ((142–145, n = 1–4)	[P4(NMe)6] (131), S or [P4(NMe)6] (131), S/CS2, −20 °C, 12 h	P88–93
[{(CO)3NiP}4(NMe)2] (146)	[P4(NMe)6] (131), [Ni(CO)4]/3 h	P94
[{(CO)3NiAs}4(NMe)2] (147)	[As4(NMe)6] (134), [Ni(CO)4]/CHCl3, 3 h, 5 min	P94
[(PNSiMe3)4(NMe)6] (148)	[P4(NMe)6] (131), Me3SiN3/toluene, 100 °C, 12 weeks	P95
[(PNPPh3)4(NMe)6] (149)	[(PNSiMe3)4(NMe)6] (148), Ph3PBr2/MeCN, 55 °C, 3 days	P95
Na10[P4(NH)6N4](NH2)6(NH3)0.5 (150)	P3N5, NaNH2/600 °C, 5 days	A96
Rb8[(PNH)4N6](NH2)2 (151)	P3N5, RbNH2/400 C, 5 days	A97

^aAr^Me6 = C₆H₃-2,6(C₆H₂-2,4,6-Me₃)₂.

Adamantane-type compounds with group 2–6 elements in the Q-position and group 16 atoms in the E-position^a.

Compound	Reagents/conditions	Method
Na2[(BeOH)4(OH)6] (152)	BeSO4, Ba(OH)2, NaOH/H2O, pH 13.2, 18 h	C98
[(μ4-O)Ba4(μ-OC6H2(CH2NMe2)3–2,4,6)6] (153)	K[(OC6H2(CH2NMe2)3-2,4,6), BaI2/toluene	K99
[(μ4-O)Ba4{OB(mes)2}6] (154)	(mes)2BOH, [Ba{N(SiMe3)2}2]2	C100
[(μ4-S)(TpMe2Y)4(SBn)6] (155)	S, [TpMe2YBn2(thf)]/THF, RT, 18 h	C101
[{Ti(TACN)}4O6]Br4 (156)	TiO(acac)2, 9aneN3, NaBr/Me2CO, H2O, 50 °C, 30 min	I102
[{Ti(dmso)3}4O6]Cl4 (157)	Na2S4, PPh4, TiCl4/DMSO, RT	C103
[(TiCp*)4O6] (158)	Cp*TiCl3, NH4OH/toluene, RT, 3 days or Cp*Ti(OMe)3/H2O, RT	I104,105
[(TiCpxPh)4O6] (159)	CpxPhTi(OME)3/Me2CO, H2O, 100 °C, 30 min	I106
[{Ti(η5-C5Me4SiMe2NHNMe2)}4O6] (160)	[(η5-C5Me4)SiMe2(NNMe2)]Ti(NMe)2/H2O, toluene, RT, 5 h	I107
[{Ti(OHF)}4O6] (161)	[(OHF)Ti(OMe)3]/Me2CO, H2O 56 °C	I106
[{Ti(η5-C5Me4SiMe3)}4O6] (162)	(η5-C5Me4SiMe3)2Ti(O)/pentane, RT, 2 weeks	J108
[{Ti(η5-C5Me4SiMe2Ph)}4O6] (163)	(η5-C5Me4SiMe2Ph)2Ti(O)/pentane, RT, 2 weeks	J108
[{Ti(η5-C5Me4iPr)}4O] (164)	(η5-C5Me4iPr)2Ti(O), Na2O2/THF, RT, overnight	I108
[Ti4(dmae)6(OH)(O)6Cu6(benzoate)9] (165)	Cu(benzoate)2·2H2O, Ti(dmae)4/toluene, RT, 2 h	C109
[Ti4(dmae)6(OH)(O)6Cu6(2-methylbenzoate)9] (166)	Cu(2-methylbenzoate)2·2H2O, Ti(dmae)4/toluene, RT, 2 h	C109
[{Ti(thf)}4O6Fe2(TFA)8(thf)2] (167)	[Fe3O(OAc)6(H2O)3]NO3, [(EtOEtO)4Ti], TFA/THF, RT, 1 h	J110
[{Ti(thf)}4O6Cd2(TFA)8(thf)2] (168)	[(OAC)2Cd(H2O)2], [Ti{iPrO)4], TFA/THF, RT, 4 h	C111
[Co(NH3)6]3[Ti4O6(Hcit)3(cit)] (169)	[Ti{iPrO)4], H4cit, [Co(NH3)6]Cl3/THF, H2O, 90 °C 1 h	I112
Na9[Ti4O6(Hcit)3(cit)] (170)	[Co(NH3)6]3[Ti4O6(Hcit)3(cit)] (169)/ion exchange chromatography	O112
[(μ4-O){Zr(acac)}4{Zr(OMe)(acac)}(DBcat)3(OMe)3] (171)	[Zr2(acac)4(DBcat)2]/CH2Cl2, MeOH, H2O, RT	I113
[(VCp*)4O6] (172)	[Cp*V(O)(μ-O)]3, PMe2Ph/THF	J114
[{HBO-3,5-(tBu)2NbCl}4O6] (173)	HBO-3,5-(tBu)2NbCl4, H2O/Toluene, THF, RT, 12 h	I115
[K-18-crown-6]4[(TaCl3)4O6] (174)	K2S5, TaCl5, 18-crown-6, H2O/CH2Cl2, RT, 20 h	I116
[(Cp*Cr)4(OH)6][Cp*Cr(CO)3] (175)	[(Cp*)2Cr2(CO)4]/H2O, toluene, 111 °C, 24 h	I117
[{(Cp*)Cr}4(OH)6][BF4]2 (176)	[(Cp*Cr)4(OH)6][Cp*Cr(CO)3] (175), H[BF4]	J117
[{Cr(tach)}4(OH)6](ClO4)n(CF3SO3)6–n (177)	[Cr(tach)(CF3SO3)3], NaOH,/H2O	I118
(enH2)[Cr4(OH)4(hpdta)2] (178)	H5hpdta, en, CrCl3/H2O, 85 °C, 24 h	K119
[{MoO(IPAP)}4O6] (179)	1. HIPAP, [MoO2Br2(DMSO)2], NEt3, PMe3/MeOH, RT, 18 h	I120
	2. PMe3/toluene, RT, 18 h
[{W(O)(tdmap)}4O6] (180)	[W(O)(OPri)4], Htdmap/toluene, H2O, iPrOH, reflux, 24 h	I121
[{(W(O)(S-Phoz)}4O6] (181)	[W(CO)(C2Me2)(S-Phoz)2], pyridine-N-Oxide/CH2Cl2, RT, 24 h	J124
[(WPMe2Ph)4S6] (182)	[W4(μ3-S)2(μ-S)4Cl2(PMe2Ph)6], Na(Hg)/THF, 8 h	J123

^ames = 2,4,6-Me₃-C₆H₂, Tp^Me2 = tri(3,5 dimethylpyrazolyl)borate), TACN = 1,4,7-triazacyclononane, DMSO = dimethyl sulfoxide, Cp^xPh = C₅Me₄Ph, OHF = 1,2,3,4,5,6,7,8-octahydrofluorenyl, dmae = N,N-dimethylaminoethanolate, TFA = trifluoacetic acid, H₄cit = citric acid, H₂DBcat = 3,5-di-tert-butylcatechol, HBO = 2-(2′-hydroxyphenyl)benzoxazole, tach = 1,3,5-triaminocyclohexane, en = ethylendiamine, H₅hpdta = hydroxypropanediaminotetraacetic acid, HIPAP = N-(tert-butyl)-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)-propanamide, tdmap = OC(CH2NMe₂)₃, S-Phoz = 2-(4′,4′-dimethyloxazoline-2′-yl)thiophenolate.

Adamantane-type compounds with group 7–9 elements in the Q-position and group 16 atoms in the E-position^a.

Compound	Reagents/conditions	Method
[{Mn(TACN)}4O6]Br3.5OH0.5 (183)	TACN, MnCl2, NaBr, O2/H2O	S125,126
[{Mn(TACN)}4O6](ClO4)4 (184)	Mn(NO3)2, Na2C2O4, TACN, NaClO4, NaOH, O2/MeOH, H2O, 60 °C, 3 h or TACN, [Mn4O6(bpea)4](ClO4)4 (186)/MeCN, RT, 1 h	S127–129
[{Mn(TACN)}4O6](OTf)4 (185)	Mn(OTf)2, TACN, O2/MeCN	S130
[{Mn(bpea)}4O6](ClO4)4 (186)	Mn(ClO4)2·6H2O, [nBu4N][MnO4],/MeCN, RT, 1 h	C131
[{Mn(bpea)}4O6]Br4 (187)	[nBu4N][Br], [Mn4O6(bpea)4](ClO4)4 (186)/MeCN, RT, 24 h	O131
[{Mn(bpea)}4O6]X4 ((188–192, X = [BF4], OTf, [PF6], SCN, )	[{Mn(bpea)}4O6)4]Br4 (187), NaX or KX/H2O, RT	O131
[{Mn(4,4′-Me2bpea)}4O6](ClO4)4 (193)	Mn(4,4′-Me2bpma)2·6H2O, [n-Bu4N][MnO4],/MeCN, RT, 1 h	C131
[{Mn(5,5′-Me2bpea)}4O6](ClO4)4 (184)	Mn(5,5′-Me2bpma)2·6H2O, [n-Bu4N][MnO4],/MeCN, RT, 1 h	C131
[{Mn(bpea)}4O6](ClO4)3 (195)	[Mn4O6(bpea)4](ClO4)4, [nBu4N]ClO4/MeCN, THF, electrolysis (−0.1 V), 25 min	N131
[{Mn(bpea)}4O6](X)3 (196–200, X = [BF4], OTf, [PF6], SCN, )	TACNMe, [Mn4O6(bpea)4](X)4 (188–192)/MeCN, 5 min	S131
[{Mn(dien)}2{Mn(bpea)}2O6](ClO4)4 (201)	[Mn4O6(bpea)4](ClO4)4 (186), dien/MeCN, RT, 3 h	Q129
[{Mn(Medien)}4](ClO4)4 (202)	[Mn4O6(bpea)4](ClO4)4 (186), medien/MeCN, RT, 45 min	Q129
[{Mn(R-ida)}2{Mn(bpea)}2O6] (203–206, R = Me, Bn, tBu, CPe)	[Mn4O6(bpea)4](ClO4)4 (186), [tBu4N]2[R-ida]/MeCN, RT, 30 min	Q129
[{Mn(tame)}4O5(OH)](OTf)5 (207)	tame·3HOTf, Mn(OTf)2·MeCN, Et3N, O2/MeCN, RT, 36 h	S130
[{Mn(tame)}4O6](OTf)4 (208)	[{Mn(tame)}4O5(OH)](OTf)5[Mn4O6(bpea)4](ClO4)4 (207), NEt3/MeCN	Q130
[{Mn(tame)}4O5(OH)](OTf)5 (209)	[{Mn(TACN)}4O6](OTf)4 (185), HClO4/MeCN	P130
[Mn4O4(tphpn)2](CF3SO3)2(ClO4)3 (210)	[{Mn2(μ-O)2(tphpn)}2], [Mn((HB(3,5-Me2pz)3)2](ClO4)2/MeCN, RT, 10 min	S/K132
[Et4N]2[(MnSPh)4(SPh)6] (211)	MnCl2·4H2O, PhSNa, Et4NCl·H2O/MeOH, RT, 40 min	C133
[Me4N]2[(MnSPh)4(SPh)6] (212)	MnCl2·4H2O, PhSNa, Me4NCl/MeOH, RT, 40 min	C133
[Et4N]2[(MnBr)4(SPh)6] (213)	MnBr2, NaSPh, [Et4N]Br/MeCN, RT, 2 h	C134
[Me4N]2((MnCl)4(SiPr)6] (214)	[Me4N]2(Mn2(SiPr)6], MnCl2/MeCN, 35 °C, 5 h	J135
[Me4N]2((MnBr)4(SeiPr)6] (215)	[Me4N]2(Mn2(SeiPr)6], MnBr2/MeCN, RT, 12 h	J135
[{Mn(BMAP)}3(MnCl)3]Cl (216)	H2BMAP, MnCl2/MeOH, 60 °C, 5 min	K136
[nBu4N]4[{Fe2(HXMeCG)}2O2(OH)2] (217)	FeCl3, [nBu4N]Cl, NaOH, H5HMeXCG/H2O	K137
(HPy)3[{Fe2(HPhXCG)}2O(OH)3] (218)	Na3H2HPhXCG, Py, Fe(NO3)3/MeOH, RT, 1 month	K138
(enH2)1.5[Fe4O(OH)3(hpdta)2] (219)	H5hpdta, Fe(NO3)3, en, dma/H2O, 3 days	K139
[{Fe2(bpbp)}2O2(OH)2](ClO4)4 (220)	Hbpbp, Fe(ClO4)3/THF, H2O, RT, 2 days	I140
[(Fe2{(TACN)CH2}2CHOH)O(OH)]2[PF6]4 (221)	{(TACN)CH2}2CHOH, FeCl3, NaOAc, NEt3, K[PF6]/iPrOH, 24–36 h	K141
[Fe4(N-Et-HPTB)2O4][BF4]2 (222)	[Fe2(N-Et-HPTB)(dmf)4][BF4]3, O2/DMF	K142
[{Fe(tBuOH)}4(dppoe)4(OH)6][PF6]2Cl4 (223)	[closo-1,12-C2B11H10(CN)2], [(Cp)(dppe)FeCl], [NH]4[PF6], tBuOH/THF, 66 °C, 18 h	J143
[{Fe(TACN)}4O2(OH)4]X4 (224–225, X = I, CIO4)	NaX, [(TACN)2Fe2(acac)2(O)](ClO4)2/Me2CO, H2O, 2 weeks	I144
[{Fe(TACN)}4O(OH)5](I)4I3 (226)	[(TACN)FeCl3], KI/H2O, Py, 72 h	D145
[{Fe(TACN)}4O2(OH)]Br4 (227)	[(TACN)FeCl3], NaBr/H2O, 25 °C, pH = 10.28	D146
[R4N]2[(FeSPh)4(SPh)6] (228–229, R = Me, Et)	FeCl2, NaSPh, [R4N]Cl/MeOH	C147,148
[Me4N]2[(FeSEt)4(SEt)6] (230)	FeCl2, NaSEt, [Me4N]Br/MeOH, 2 h	C149
[Ph4P]2[(FeCl)4(SPh)6] (231)	FeCl2, [Ph4P]2[Fe(SPh)4]/MeCN, 30 min	C150
[Ph4P]2[(FeBr)4(SPh)6] (232)	FeBr2, [Ph4P]2[Fe(SPh)4]/MeCN, 30 min	C150
[Et4N]2[(FeBr)4(SBn)6] (233)	FeCl2, NaSBn, [Et4N]Br/MeCN	C151
[{Fe(BMAP)}3(FeCl)3]Cl (234)	H2BMAP, FeCl2·4H2O/MeOH, 60 °C, 5 min	K136
[(RuPPh3)4S6] (235)	RuCl2(DMSO)4, PPH3, (SiMe3)2S/THF, −50 °C	C152
[Co4(HMPM)2](ClO4)2 (236)	Co(ClO4)2, H3HMPM, Et3N/MeOH, RT	K153
[Me4N]2[{Co(SPh)}4(SPh)6] (237)	PhSH, Et3N, Co(NO3)2, [Me4N]Cl/EtOH	C154
[Cy2NH2]2[{Co(SPh)}4(SPh)6] (238)	PhSH, Cy2NH, Co(NO3)2, [Me4N]Cl/EtOH	C154
[Et4N]2[{Co(SEt)}4(SEt)6] (239)	NaSEt, CoCl2, [Et4N]Cl/MeCN	C149
[tBu4N]2[{Co(Cl)}4(SPh)6] (240)	[tBu4N][CoCl3(PPh3)], PhSSiMe3/toluene, 3 h	C155
[Et4N]2[{Co(Cl)}4(SPh)6] (241)	Na, PhSH, CoCl2, [Et4N]Cl/MeOH, RT	C156
[{Co(Cl)}2(CoPPh3)2(SPh)6] (242)	[CoCl2(PPh3)2], PhSSiMe3/THF, 3 h	C155
[{Co(Cl)}2(CoPPh3)(CoPOPh3)(SPh)6] (243)	[CoCl2(PPh3)2], PhSSiMe3, O2/THF, 3 h	C155

^abpea = N,N-bis(2-pyridylmethyl)ethylamine, = [3,5-(CF₃)₂C₆H₃]₄B]⁻, dien = diethylenetriamine, medien = N′-methyldiethylenetriamine, R-ida = N-(R)iminodiacetate, ^CPe = cyclopentane, tame = tert-amyl methyl ether, Htphpn = N,N,N′,N′-tetra-(2-methylpyridyl)-2-hydroxypropanediamine, pz = pyrazolyl, H₂BMAP = 2-[bis(2-mercaptoethyl)aminomethyl]pyridine, Py = pyridine, H₅HMeXCG = N,N′-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine), H₅HPhXCG = N,N′-(2-hydroxy-5-phenyl-1,3-xylylene)bis(N-(carboxymethyl)glycine), dma = N,N-dimethylacetamid, Hbpbp = 2,6-bis((N,N′-bis-(2-picolyl)amino)methyl)-4-tert-butylphenol, {(TACN)CH₂}₂CHOH = 1,3-bis(1,4,7-triaza-1-cyclononyl)-2-hydroxypropane, N-Et-HPTB = N,N,N′,N′-tetrakis(2-(1-ethylbenzimidazolyl))-2-hydroxy-1,3-diaminopropane, dppoe = 1,2-bis(diphenylphosphine oxide)ethane, dppe = 1,2-bis(diphenylphosphino)ethane, H₃HMPM = 2,6-bis[{{(1-hydroxy-2-methylpropan-2-yl)(pyridine-2-ylmethyl)}amino}methyl]-4-methylphenol.

Adamantane-type compounds with group 11 in the Q-position and group 16 atoms in the E-position^a.

Compound	Reagents/conditions	Method
[Me4N]2[Cu4(SPh)6] (244)	Cu(NO3), PhSH, nBu3N, [Me4N]Cl/EtOH, 75 °C	C157–159
[Ph4P]2[Cu4(SPh)6] (245)	[Ph4P]2[Cu(SPh)3], [Cu(MeCN)4]ClO4/MeCN, 82 °C, 5 min	J160,161
[Li(diglyme)2]2[Cu4(SPh)6] (246)	CuN(SiMe3)2, LiN(SiMe3)2, HSPh/diglyme, 110 °C, 10 min	C162
[Li(dme)3]2[Cu4(SPh)6] (247)	CuN(SiMe3)2, LiN(SiMe3)2, HSPh/DME, 84 °C, 10 min	C162
[Li(15-crown-5)thf]2[Cu4(SPh)6] (248)	CuN(SiMe3)2, LiN(SiMe3)2, HSPh, 15-crown-5/THF, slight heat, 5 min	C162
[Me4N]2[Cu4(SMe)6] (249)	[Me4N][CuCl2], NaSMe/EtOH, MeCN, 75 °C, 90 min	C159,163
[nPr4N]2[Cu4(SMe)6] (250)	Cu2O, [nPr4N]Br, NaOMe/(CH2OH)2, MeOH, MeCN, 55 °C, 1 h	C164
[Ph4P]2[Cu4(SEt)6] (251)	Cu2O, EtSH, [Ph4P]Br, NaOMe/(CH2OH)2, 55 °C	C165
[Et4N]2[Cu4(SC6H4-p-Cl)6] (252)	Cu(NO3)2, HSC6H4-p-Cl, nBu3N, [Et4N]Cl/EtOH, MeOH, MeCN, 50 °C to 4 °C, 18 h	C166
[Et4N]2[Cu4{S(o-tBuC6H4)}6] (253)	CuCl, HS(o-tBuC6H4, NaH, [Et4N]Cl/DMF	C167
[Et4N]2[Cu4(SiPr)6] (254)	CuCl, HSiPr, NaH, [Et4N]Cl/THF, 24 h	C168
[K(Me2phen)3]2[Cu4(SBn)6] (255)	CuCl, KSBn, Me2phen/THF	C169
[Et4N]2[Cu4(SPh)6] (256)	[(NEt4]4[(SPh)4(CuBr)6] (847), HSPh, Et3N/DMF, 15 min	J170
[(nBu)4N]2[Cu4(SCH2CH2OH)6] (257)	(CuSCH2CH2OH)n, [(nBu)4N]OH/H2O	I171
[Cu(BIK)2]2[Cu4{S(o-tolyl)}6] (258)	BIK, HS(o-tolyl), Cu anode, [nBu4N]ClO4/MeCN, electrolysis	N172
[Me4N]2[Cu4(SePh)6] (259)	CuCl, PhSeH, Et3N, [Me4N]Cl/DMF, MeOH	C173
[tBu3PH]2[Cu4(TePh)6] (260)	[(tBu3P)3(CuTePh)4], Me3SiTePh, Me3GaOEt2/THF	J174
[Et3PPh][μ3-Cu(CuPEt3)3Cu(TePh)6] (261)	PEt3, CuCl, Te(Ph)SiMe3/Pentane, RT, 18 h	C175
[Ph4P]2[Cu4{o-(SCH2)2C6H4}3] (262)	Cu(NO3)2, o-(HSCH2)2C6H4, NEt3, [Ph4P]Br/EtOH, 5 h	C176
[Ph4P]2[Cu4(SCH2CH2S)3] (263)	CuCl, HSCH2CH2SH, NEt3, [Ph4P]Br/MeCN, 5 h	C177,178
[(Me3P)4Cu]2[Cu4(SCH2CH2S)3] (264)	[CuSCH2CH2SCu], PMe3/PhMe, 90 °C, 1.5 h	C179
[Ph4P]2[Cu4{S(CH2)3S}3] (265)	HS(CH2)3SH, Cu2O, [Ph4P]Br, NaOMe/(CH2OH)2, MeOH, 55 °C, 1 h	C178
[Me4N]2[Cu4{S(CH2)3S}3] (266)	HS(CH2)3SH, Cu2O, [Me4N]Cl, NaOMe/MeCN, MeOH, 50 °C, 1 h	C178
[Et4N]2[Cu4{S(CH2)3S}3] (267)	HS(CH2)3SH, Cu2O, [Et4N]Br, NaOMe/MeCN, MeOH, 50 °C, 45 min	C178
[Et4N]2[Cu4(SCH2CH2S)3] (268)	HSCH2CH2SH, Cu2O, [Et4N]OH/MeCN, MeOH, 50 °C	C178
[Me3NCH2Ph]2[Cu4(SCH2CH2S)3] (269)	HSCH2CH2SH, Cu2O, [Me3NCH2Ph]Cl, NaOMe/glycerol, MeOH, 45 °C	C178
[Me4N]2[Cu4(C8H6S8)3] (270)	[Cu(MeCN)4][PF6], C8H8S8, [Me4N]OH/THF, Me2CO, MeOH, 3 days	C180
[Ph4P]2[Cu4(tpdt)3] (271)	CuCl2, 5,6-thieno[2,3-d]-1,3-dithiol-2-one, KOMe, [Ph4P]Br/MeOH, 1 h	C181
[Ph4P]2[Cu4(α-tpdt)3] (272)	CuCl2, thieno[3,4-d]-1,3-dithiol-2-thione, KOMe, [Ph4P]Br/MeOH, 1 h	C181
[(Me3P)4Cu][Cu4(SCH2CH2S)3(CuPPh3)] (273)	[(Me3P)4Cu]2[Cu4(SCH2CH2S)3]/THF	J179
K[Ph4P][Cu4(tBu2DED)3] (274)	K4[Cu8(tBu2DED)6], [Ph4P]Cl, S/Me2CO, EtOH	J182,183
[Ph4P]2[Cu4(S4)3] (275)	S, H2S, Cu(MeCO2)2, [Ph4P]Br, NH3/MeCN	C184
[Cu4{SC(NH2)2}6](NO3)4 (276)	CuNO3, SC(NH2)2 HNO3/H2O	C185
[Cu4{SC(NH2)2}6](SO4)2 (277)	CuSO4, SC(NH2)2, HOAc/H2O, 80°	C186
[Cu4{SC(NH2)2}6](HSO4)2SO4 (278)	CuSO4, SC(NH2)2, H2SO4/H2O, 80 °C	C186,187
[Cu4(H4pymtH)6](ClO4)4 (279)	[Cu(C2H4)ClO4], H4pymtH, C2H4/MeOH	C188
[Cu4{SC(NH2)NHCH2CH CH2}6](OTf)4 (280)	Cu(OTf)2, SC(NH2)NHCH2CH CH2/C6H6, 20 min	C189
[{CuSC(NH2)2}3Cu{SC(NH2)2}6](NO3)4 (281)	CuNO3, SC(NH2)2, HNO3/H2O	C185
[{CuSC(NH2)2}Cu3{SC(NH2)2}6](SO4)2 (282)	CuSO4, SC(NH2)2, H2SO4/H2O	C190
[{CuSC(NH2)2}(CuNO3)Cu2{SC(NH2)2}6](SO4)(NO3) (283)	Cu(NO3)2, SC(NH2)2/H2O, 80 °C to 5 °C, 5 days	C191
[(CuI)4{SC(NH2)NHEt}6] (284)	CuI, SC(NH2)NHEt/EtOH, 50 °C, 3 h	C192
[(CuI)4{SC(NH2)2}6] (285)	CuI, SC(NH2)2, KI/H2O, 80 °C	C193
[(CuCl)4{SC(NH2)NHCH2CH CH2}6] (286)	CuCl2, Cu electrode, SC(NH2)NHCH2CH CH2, HCl/EtOH, 0.2 V, 0.13 mA	N194
[Cu4{(SPPh2)2N}3][CuICl2] (287)	1. NaN(SPPh2)2, CuCl2/H2O	J195,196
	2. CCl4, CH2Cl2
[Cu4{(SPPh2)2N}3][BF4] (288)	[Cu(MeCN)4][BF4], (SPPh2)2NH/CH2Cl2, 1 h	C197
[Cu4{(SPPh2)2N}3]I3 (289)	Cu, (SPPh2)2NH·I2/Et2O, 2 days	C198
[Cu4{(SePPh2)2N}3][BF4] (290)	[Cu(MeCN)4][BF4], (SePPh2)2NH/CH2Cl2, 1 h	C197
[Cu4(O3N4)2](ClO4)2 (291)	Cu(ClO4)2, H3O3N4, Et3N/MeOH	C199
[Et4N]2[Ag4(SC6H4-p-Cl)6] (292)	AgNO3, HSC6H4-p-Cl, nBu3N, [Et4N]Cl/EtOH, MeOH, MeCN, 50 °C to 4 °C, 18 h	C166
[Ph4P]2[Ag4{o-(SCH2)2C6H4}3] (293)	AgNO3, Na2o-(SCH2)2C6H4, [Ph4P]Br/MeOH, 5 h	C200
[nBu4N]2[Ag4(FcSe2)3] (294)	AgCl, Fc(SeSiMe3)2, [nBu4N]Br/THF	C201
[Et4N][Br@Ag8(2-TBI)12(SO4)2][Ag4(2-TBI)6(SO4)3]2 (295)	Ag2SO4, 2-TBI, [Et4N]Br/MeCN, DMF, sonification, 120 °C, 2 days	B/L202
[Ph4P]2[Ag4(C4H3STe)6] (296)	1. Te, [Ph4P]Br, thiophene, nBuLi/THF	C203
	2. AgNO3/DMF
[nPr4N]2[Ag4(Se4)3] (297)	AgNO3, Na2Se5, [nPr4N]Cl/DMF	C204
[Ag4{(SePPh2)2N}3](OTf) (298)	Ag(OTf), K{(SePPh2)2N}/CH2Cl2, 30 min	C205
[(AgPPh3)4(Mbis)3](OTf)4 (299)	[Ag(OTf)(PPh3)], Mbis/Me2CO, 1 h	C206

^aMe₂phen = 2,9-dimethyl-1,10-phenanthroline, BIK = bis(2-methyl-imidazole-2-yl)ketone, ^tBu₂DED = 1,1-dicarbo-tert-butoxy-2,2-ethylenedithiolate, tpdt = 3,4-thiophenedithiolate, α-tpdt = 2,3-thiophenedithiolate, H₄pymtH = 3,4,5,6-tetrahydropyrimidine-2-thione, H₃O₃N₄ = 1-Me-4-OH-3,4-bis(CH₂N(CH₂C₅H₄N)(CMe₂CH₂OH)–C₆H₂, Fc = ferrocenyl, 2-TBI = 2-thiobenzimidadzol, Mbis = 1,1′-methylenebis(3-methylimidazoline-2-selone).

Adamantane-type compounds with group 12 in the Q-position and group 16 atoms in the E-position^a.

Compound	Reagents/conditions	Method
[Et3NH]2[(ZnSPh)4(SPh)6] (300)	HSPh, Zn anode, Et3N, [Et4N]ClO4/MeCN, electrolysis or NaSPh, ZnCl2 [Et3NH]Cl/MeOH, 0 °C, 90 min	N,C207–209
[Me4N]2[(ZnSPh)4(SPh)6] (301)	HSPh, Zn(NO3)2, Et3N, [nPr4N]Cl/MeOH, Me2CO, 3 days	C210
(DAMS)2[(ZnSPh)4(SPh)6] (302)	HSPh, Zn(NO3)2, Et3N, (DAMS)I/MeOH	C211
[Ru(2,2′-bipy)3][(ZnSPh)4(SPh)6] (303)	Cd(SPh)2, SC(NH2)2, [Ru(2,2′-bipy)3Cl2]/MeCN, H2O, 85 °C, 10 days	B212
[Et4N]2[(ZnSBn)4(SBn)6] (304)	BnSH, NaOMe, Zn(NO3)2, [Et4N]2Cl/MeOH, 2 h	C213
[Ph4P]2[(ZnSBn)4(SBn)6] (305)	BnSH, NaOMe, Zn(NO3)2, [Ph4P]2Cl/MeOH, 2 h	C213
[Et3NH][Me4N][(ZnSC6H4-4-Cl)4(SC6H4-4-Cl)6] (306)	HSC6H4-4-Cl, Et3N, Zn(NO3)2 [Me4N]Cl/MeOH, 0 °C, 30 min	C209
[Me4N]2[(ZnSC6H4-4-Cl)4(SC6H4-4-Cl)6] (307)	HSC6H4-4-Cl, NaOH, ZnCl2 [Me4N]Cl/MeOH, 0 °C, 2 h	C209
[Et3NH][(ZnSC6H4-4-Cl)4(SC6H4-4-Cl)6] (308)	HSC6H4-4-Cl, Et3N, Zn(NO3)2 [Et3NH]Cl/MeOH, 0 °C, 30 min	C209
[Me4N]2[(ZnSePh)4(SePh)6] (309)	Na, HSePh, Zn(NO3)2, Et3N, [nPr4N]Cl/H2O, MeOH, MeCN, 60 °C	C214,215
[Et3NH][(CdSPh)4(SPh)6] (310)	HSPh, Cd anode, Et3N, [Et4N]ClO4/MeCN, electrolysis	N208
[Me4N]2[(CdSPh)4(SPh)6] (311)	HSPh, Cd(NO3)2, Et3N, [Me4N]Cl/MeOH	C216
[Et4N]2[(CdSPh)4(SPh)6] (312)	HSPh, CdCl2, Et3N/MeOH, H2O	C148,217
(DAMS)2[(CdSPh)4(SPh)6] (313)	(DAMS)I, PhSH, Et3N, Cd(SCN)2,/MeOH, 10 min	C218
[M(phen)3][(CdSPh)4(SPh)6] (314–316, M = Ru, Fe, Ni)	[Me4N][(CdSPh)4(SPh)6] (311), M(phen)3Cl2/MeCN, 30 min	O219
[Et4N]2[(CdSCy)4(SCy)6] (317)	NaSCy, CdCl2, [Et3N]Cl/EtOH, MeCN	C220
[Et3NH]2[(CdSC6H4-4-Me)4(SC6H4-4-Me)6] (318)	Cd[ClO4]2, SC6H4-4-Me, Et3N, [Me4N]Cl/MeOH, 1 h	C221
[Me4N][(CdSePh)4(SePh)6] (319)	NaSePh, Cd(NO3)2, [Me4N]Cl/MeOH, H2O, MeCN, 80 °C	C215,222
[Me4N][Cd4(SPh)10−n(SMe)n] (320–322, n = 8–10)	[Me4N][(CdSPh)4(SPh)6] (311), Me2S2/Me2CO	Q222
[Me4N][Cd4(SPh)10−n(SnBu)n] (323–329, n = 4–10)	[Me4N][(CdSPh)4(SPh)6] (311), nBu2S2/Me2CO	Q222
[Me4N][Cd4(SPh)10−n(SBn)n] (330–333, n = 7–10)	[Me4N][(CdSPh)4(SPh)6] (311), Bn2S2/Me2CO	Q222
[Me4N][Cd4(SPh)10−n{S(2-C6H4Me)}n] (334–344, n = 0–10)	[Me4N][(CdSPh)4(SPh)6] (311), (2-C6H4Me)2S2/Me2CO	Q222
[Me4N][Cd4(SePh)10−n(SnBu)n] (345–350, n = 5–10)	[Me4N][(CdSePh)4(SPh)6] (319), nBu2S2/Me2CO	R222
[Me4N][Cd4(SPh)10−n(TePh)n] (351–353, n = 8–10)	[Me4N][(CdSPh)4(SPh)6] (311), Ph2Te2/Me2CO	R222
[Me4N][Cd4(SePh)10−n(TePh)n] (354–357, n = 7–10)	[Me4N][(CdSePh)4(SePh)6] (319), Ph2Te2/Me2CO	R222
[Me4N][Cd4(SPh)10−n(SePh)n] (358–368, n = 0–10)	[Me4N][(CdSPh)4(SPh)6] (311), [Me4N][(CdSePh)4(SePh)6]/	R222
[Me4N][CdxZn4−n(SPh)10] (369–371, n = 2–4)	[Me4N][(CdSPh)4(SPh)6] (311), [Me4N]2[(ZnSPh)4(SPh)6]/Me2CO	R222
[(MTab)4(Tab)6][PF6]8 (372–373, M = Zn, Cd)	TabH[PF6], M(OAc)2/MeCN, DMF, MeOH, 70 °C, 1 h	C223
[Me4N]2[(ZnCl)4(SPh)6] (374)	[Me4N]2[(ZnSPh)4(SPh)6] (301), PhICl2/MeCN, 10 min	Q214,224
[Me4N]2[(ZnBr)4(SPh)6] (375)	[Me4N]2[(ZnSPh)4(SPh)6] (301), Br2/CCl4, Me2CO, 10 min	Q214,224
[Me4N]2[(ZnI)4(SPh)6] (376)	[Me4N]2[(ZnSPh)4(SPh)6] (301), I2/Me2CO	Q214,224
[nBu4N]2[(ZnI)4(SnPr)6] (377)	Zn(SnPr)2, ZnI2, [nBu4N]I/CH2Cl2	C225
[Et4N]2[(MX)4(SR)6] (378–406, R/M/X = iPr/Zn/Cl, Br, I; iPr/Cd/Cl, Br, I; Me/Zn/Br, I; nPr/Zn/I; nBu/Zn/I; nBu/Cd/I, Et/Zn/Cl, Br, I; Et/Cd/Cl, Br, I, Bn/Zn/Cl, Br, I; Bn/Cd/Cl, Br, I, secBu/Zn/Cl, Br, I; secBu/Cd/Cl, Br, I)	MX2, [Et4N]X, M(SR)2/CH2Cl2, 1 h	C226
[Me4N]2[(ZnCl)4(SePh)6] (407)	[Me4N]2[(ZnSePh)4(SePh)6] (309), PhICl2/MeCN, 10 min	Q214
[Me4N]2[(CdCl)4(SPh)6] (408)	[Me4N]2[(CdSPh)4(SPh)6] (309), PhICl2/MeCN, 10 min	Q214
[R4N]2[(CdCl)4(SePh)6] (409–410, R = nPr, nBu)	CdCl2, (cat)Cl, Cd(SPh)2/CH2Cl2, 1 h	C227,228
[nPr3PH]2[(CdCl)4(SeFc)6] (411)	n Pr3P, CdCl2, Me3SiSeFc/THF, 10 min	C229
[Me4N]2[(CdBr)4(SPh)6] (412)	[Me4N]2[(CdSPh)4(SPh)6] (311), Br2/CCl4, Me2CO, 10 min	Q214
[Me4N]2[(CdI)4(SPh)6] (413)	[Me4N]2[(CdSPh)4(SPh)6] (311), I2/Me2CO	Q214
(DAMS)2[(CdI)4(SPh)6] (414)	(DAMS)I, PhSH, Et3N, Cd(NO3)2,/MeOH, 10 min	C218
[Et4N]2[(CdI)4(SnPr)6] (415)	CdI2, [Et4N]I, Cd(SnPr)2/CH2Cl2	C225
[Me4N]2[(CdCl)4(SePh)6] (416)	[Me4N]2[(CdSePh)4(SePh)6] (319), PhICl2/MeCN, 10 min	Q214
[Me4N]2[(CdBr)4(SePh)6] (417)	[Me4N]2[(CdSePh)4(SePh)6] (319), Br2/CCl4, Me2CO, 10 min	Q214
[Me4N]2[(CdI)4(SePh)6] (418)	[Me4N]2[(CdSePh)4(SePh)6] (319), I2/Me2CO	Q214
[Et4N]2[(HgX)4(SnPr)6] (419–421, X = Cl, Br, I)	HgX2, [Et4N]X, Hg(SnPr)2/CH2Cl2	C225
[Et4N]2[(HgX)4(SePh)6] (422–424, X = Cl, Br, I)	HgX2, [Et4N]X, Hg(SePh)2/CH2Cl2	C225
[Mg(CH2{P(O)Ph2}2)3][(HgX)4(SePh)6] (425–427, X = Cl, Br, I)	Hg(SePh)2, MgX2, CH2{P(O)Ph2}2/DMF, 1 h	C230
[M(CH2{P(O)Ph2}2)3][(HgBr)4(SePh)6] (428–430, M = Fe, Co, Ni)	Hg(SePh)2, MBr2, CH2{P(O)Ph2}2/DMF, 1 h	C230
[Et4N]2[(HgX)4(TePh)6] (431–433, X = Cl, Br, I)	HgX2, [Et4N]X, Hg(TePh)2/CH2Cl2, 30 min	C225
[Et4N]2[(CdI)n(ZnI)4−n(SnPr)6] (434–436, n = 1–3)	[Et4N]2[(CdI)4(SnPr)6] (415), [nBu4N]2[(ZnI)4(SnPr)6] (377)/CH2Cl2	R225
[Et4N]2[(HgI)n(CdI)4−n(SnPr)6] (437–439, n = 1–3)	[Et4N]2[(HgI)4(SnPr)6] (421), [Et4N]2[(CdI)4(SnPr)6] (415)/CH2Cl2	R225
[Et4N]2[(HgI)n(ZnI)4−n(SnPr)6] (440–442, n = 1–3)	[Et4N]2[(HgI)4(SnPr)6] (421), [nBu4N]2[(ZnI)4(SnPr)6] (377)/CH2Cl2	R225
[Me4N]2[(ZnSPh)2(ZnX)2(SPh)6] (443–444, X = Cl, Br)	HSPh, Zn(NO3)2, Et3N, [Me4N]X/MeOH, Me2CO, 10 days	C210
[Me4N]2[(ZnSPh)3(ZnCl)(SPh)6] (445)	HSPh, Zn(NO3)2, Et3N, [nPr4N]Cl/MeOH, Me2CO, 10 days	C210
[Et3NH]2[(CdCl)3(p-tBu-C6H4SCd)(p-tBu-C6H4S)6] (446)	p-tBu-C6H4SH, Et3N, CdCl2/MeOH, 19.5 h	C231
[Me4N]2[(CdSPh)3(CdCl)(SPh)6] (447)	HSPh, Cd(NO3)2, NEt3, [Me4N]Cl/MeOH, 1 h	C232
[(Ph3P)2N]2[Hg(HgI)3(SePh)6] (448)	HgI2, [(Ph3P)2N]I, Hg(SePh)2/CH2Cl2	C225
[(HgPPh3)2(HgX)2(TeoPy)6] (449–451, X = Cl, Br, I)	o Py2Te2, Li[BH4], Hg(OAc)2, HgX2, PPh3/DMF, EtOH, THF, 2 h	C233
[(HgPPh3)2(HgSePh)2(SePh)6] (452)	HgBr2, PPh3, HSePh, Et3N/MeCN, 3 days	C234
[(CdPPh3)4(SPh)6][ClO4]2 (453)	[Cd(PPh3)2(ClO4)2], Cd(SPh)2, PPh3/CH2Cl2, 20 min	C235
[(CdPPh3)4(SePh)6][ClO4]2 (454)	[Cd(PPh3)2(ClO4)2], Cd(SePh)2, PPh3/CH2Cl2, 20 min	C235
[(HgPPh3)4(EPh)6][ClO4]2 (455–456, E = S, Se)	[Hg(PPh3)2(ClO4)2], Hg(EPh)2, PPh3/CHCl3, 10 min	C236,237
[(HgPPh3)4(SMe)6][ClO4]2 (457)	[Hg(PPh3)2(ClO4)2], Hg(SMe)2, PPh3/CHCl3, 10 min	C236
[(HgPPh3)4(SEt)6][ClO4]2 (458)	[Hg(PPh3)2(ClO4)2], Hg(SEt)2, PPh3/CH2Cl2, 10 min	C236
[(HgAsPh3)4(SPh)6][ClO4]2 (459)	[Hg(AsPh3)2(ClO4)2], Hg(SPh)2, AsPh3/CHCl3, 10 min	C236
[(HgPEt3)4(SPh)6][ClO4]2 (460)	[Hg(PEt3)2(ClO4)2], Hg(SPh)2, PEt3/Me2CO	C236
[(HgPEt3)4(SePh)6][ClO4]2 (461)	[Hg(PEt3)2(ClO4)2], Hg(SePh)2, PEt3/CHCl3, 10 min	C236
[Cd(CdPPh3)3(SnPr)6][ClO4]2 (462)	[Cd(PPh3)2(ClO4)2], Cd(SnPr)2, PPh3/CH2Cl2, 20 min	C235
[Cd2(CdPPh3)2(SR)6][ClO4]2 (463–464, R = Cy, iPr)	[Cd(PPh3)2(ClO4)2], Cd(SR)2, PPh3/CH2Cl2, 20 min	C235
[2.2.2]-cryptH2[(ZnI)4(MeO)6] (465)	[2.2.2]-crypt, ZnI2/MeOH, 1 day	C238
[Zn4(POPYH)3Cl] (466)	POPYH4, Et3N, ZnCl2/MeCN, 70 °C, 3 h	K239

^aDAMS = trans-4-(4-dimethylamino-styryl)-N-methyl-pyridinium, bipy = bipyridine, ⁿPr = normal propyl, ^secBu = secondary butyl, phen = 1,10-phenanthroline, ^oPy = ortho-pyridyl, Tab = 4-(trimethylammonio)benzenethiolate, [2.2.2]-crypt = 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, POPYH₄ = N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide.

Adamantane-type compounds with group 13 elements in the Q-position and group 16 atoms in the E-position^a.

Compound	Reagents/conditions	Method
K8[Ga4S10] (467)	Ga2S3, K2S/H2O, 90 °C, 4 h	C240
K8[In4S10] (468)	In2S3, K2S/H2O, 90 °C, 4 h	C240
K8[In4Se10] (469)	In2Se3, K2S/H2O, 90 °C, 4 h	C240
[H2dap]4[Ga4Se10] (470)	Ga, Se, dap, H2O/170 °C, 5 days	B241
[(C3H7)2NH2]4[(InSH)4S6] (471)	In, S, dipropylamine/180 °C, 5 days	B242
[NHMe3]4[(InSH)4S6] (472)	In, S, NMe3/EtOH, 140 °C, 5 days	B243
{[Ni(tepa)]2SO4}[Ni(tepa)(GaSH)4S6] (473)	Ga, NiS, tepa/H2O, 180 °C, 7 days	B241
[(AlNMe3)4S6] (474)	Me3N·AlH3, (SiMe3)2S/toluene, 110 °C, 5 days	D244
[(GaNH3)4S6] (475)	Ga, S, [NMe4]Cl, urea/N2H4·H2O, 180 °C, 8 days	B243
[(4-Me2N–C5H4NGa)4S6] (476)	1. (4-Me2N–C5H4N)GaHCl2, (SiMe3)2S/MeCN, −25 °C to RT, 29 h	D245
	2. 4-Me2N–C5H4N/MeCN, 82 °C, 8 h
[(AlI)4(SMe)4S2] (477)	1. Ga, GaI3, AlI3/200 °C	A247
	2. Me2S2/110 °C
[(GaI)4(SMe)4S2] (478)	Me2S2, Ga2I4/110 °C	A246
[(TACNIn)4(OH)6](ClO4)6 (479)	InBr3, NaOH, NaClO4, TACN/H2O, 12 h	C248
[(TACNIn)4(OH)6](S2O6)3 (480)	InBr3, NaOH, NaS2O6, TACN/H2O, 12 h	C248
[(BuGa)4(OH)6][CHB11Br6Me5] (481)	[2,6-(2,6-Mes2C6H3)2C5H3GanBu][CHB11Br6Me5], H2O/C6D6, 16 h	I249
[{(Me3Si)3Si}4Ga4O(OH)5][{(CO)3Fe}3{GaSi(SiMe3)3}2{GaFe(CO)4}] (482)	[(Me3Si)3SiGaCl]4, Na2Fe(CO)4·2 dioxane, NaOH/Et2O	J250
[{(Me3Si)3CAl}4O2(OH)4] (483)	1. AlMe2Cl, [(Me3Si)3CLi·2 thf]/THF, hexane, 15 h	I251
	2. H2O/THF, −10 °C, 1 h
[{(Me3Si)3CGa}4O2(OH)4] (484)	1. GaMe2Cl, [(Me3Si)3CLi·2 thf]/THF, hexane, 15 h	I251
	2. H2O/THF, 24 h, 150 °C, 4 h
[enH2][Al4(OH)4(hpdta)2] (485)	H5hpdta, AlCl3, en/H2O	K139
[(μ4-O){(Me3Si)3CIn}4(OH)6] (486)	1. InCl3, (Me3Si)3CLi/THF, −40 °C	I252
	2. LiAlH4/THF, −78 °C
	3. MeOH, H2O

^adap = 1,2-diaminopropane, tepa = tetraethylenepentamine

Adamantane-type compounds with purely inorganic cluster anions with group 14 elements in the Q position and group 16 atoms in the E position^a.

Compound	Reagents/conditions	Method
Na4[Si4S10] (487)	SiS2, Na2S/800 °C, 48 h	A253
Na4[Si4Se10] (488)	Na, Si, Se/800 °C	A254
K4[Si4Te10] (489)	K, Si, Te/350 to 400 °C, 17 h	A255
Na4[Ge4S10] (490)	GeS2, Na2S/H2O or GeS2, Na2S/800 °C, 48 h	A/C253,256–259
K4[Ge4S10] (491)	GeS2, K2S/H2O	C256
Rb4[Ge4S10] (492)	GeS2, Rb2S/H2O	C256
Cs4[Ge4S10] (493)	GeS2, Cs2S/H2O or S, Ge, CsOH/H2O, 150 °C, 16 h	B/C 256,260,261
Ba2[Ge4S10] (494)	GeS2, BaS/1250 °C	A253
Tl4[Ge4S10] (495)	Tl2S, GeS2/500 °C, 10 days	A262
[Me4N]4[Ge4S10] (496)	GeS2, [Me4N]HS, H2S/H2O, 150 °C, 4 days or GeS2, [Me4N]Cl, Na2CO3/H2O, 120 °C, 2 days	G/B263–266
[EtNH3]3[MeNH3][Ge4S10] (497)	1. GeO2, S, MeNH2/EtOH, 160 °C, 24 h	B281
	2. EtNH2/EtOH, 160 °C, 24 h
[Li4(H2O)16][Ge4Se10] (498)	1. LiSe2, Ge, Se/heat to melt	E282
	2. H2O
[Li4(thf)12][Ge4Se10] (499)	1. LiSe2, Ge, Se/heat to melt	E282
	2. THF
Na4[Ge4Se10] (500)	Na, Ge, Se/800 °C	A267
K4[Ge4Se10] (501)	K, Ge, Se/800 °C	A268
Rb4[Ge4Se10] (502)	Rb2CO3, Ge, Se/MeOH, 190 °C, 24 h	B269
Cs4[Ge4Se10] (503)	Cs2CO3, Ge, Se/MeOH, 190 °C to RT, 4 h	B270
Tl4[Ge4Se10] (504)	Tl2Se, GeSe2/500 to 400 °C, 9 days	A271
[Me4N]4[Ge4Se10] (505)	Ge, Se, Me4N]OH/H2O, 150 °C, 3 days	B272
[(C3H7)3NH]4[Ge4Se10] (506)	Ge, Se, N(C3H7)3/H2O, 230 °C, 20 days	B273
[Et4N]4[Ge4Te10] (507)	1. K2Te, Ge, Te/heat to melt	E274
	2. [Et4N]Br/en, 3 days
[R4N]4[Sn4E10], (508–513, R = Me, Et; E = S, Se, Te)	1. K2E, E, Sn/heat to melt	E275
	2. [R4N]Br/en, 100 °C, 12 h
[18-Crown-6-K]4[Sn4Se10] (514)	1. K, Sn, Se/heat to melt	E276
	2. 18-Crown-6/THF, en, 14 days
(K[2.2.2]-crypt)4[Sn4Se10] (515)	1. K, Sn, Se/heat to melt	E277
	2. [2.2.2]-crypt/en, NH3, -40 °C
[Me4N]4[Sn4Se10] (516)	Sn, Se, [Me4N]OH,/H2O, 150 °C, 16 days	B278
[Et4N]4[Sn4Se10] (517)	[Et4N]Br, Sn2Se3 cathode, Ni anode/en, 300 μA, 5 V, 5 days	N283
[(CHMeEt)2NH2]4[Sn4Se10] (518)	Sn, Se (CHMeEt)2NH/H2O, 160 °C, 25 days	B279
[(C3H7)2NH2]4[Sn4Se10] (519)	Sn, Se, S, (C3H7)3N/H2O, 130 °C, 20 days	B280
[18-Crown-6-K]4[Sn4Te10] (520)	1. K2Te, Sn, Te/heat to melt	E276
	2. 18-Crown-6/THF, en, 28 days
[CnH2n+1NMe3]4[Ge4S10] (521–524, n = 12, 14, 16, 18)	Na4[Ge4S10] (490), [CnH2n+1NMe3]Br/H2O, 18 h	O284
[C8H17NMe3]4[Ge4Se10] (525)	K4[Ge4Se10] (501), [C8H17NMe3]Br/Me2CO, H2O, 3 days	O285
[C9H19NMe3]4[Ge4Se10] (526)	K4[Ge4Se10] (501), [C9H19NMe3]Br/Me2CO, H2O, 45 °C, 1 day	O285
[C8H17NMe2H]4[Ge4Se10] (527)	K4[Ge4Se10] (501), [C8H17NMe2H]Cl/Me2CO, H2O, 40 °C, 1 day	O285
[CnH2n+1NMe3]4[Ge4Se10] (528–530, n = 10, 11, 12)	K4[Ge4Se10] (501), [CnH2n+1NMe3]Br/Me2CO, H2O, 80 °C, 1 day	O285
[CnH2n+1NMe3]4[Ge4Se10] (531–573, n = 14, 16, 18)	K4[Ge4Se10] (501), [CnH2n+1NMe3]Br/Me2CO, H2O, 120 °C, 3 days	O285
[(C4H9)3NH]4[Ge4Se10] (534)	K4[Ge4Se10] (501), (C4H9)3N, HCl/Me2CO, H2O, 50 °C, 3 days	O285
[CnH2n+1NH3]4[Ge4Se10] (535–538, n = 12, 14, 16, 18)	Na4[Ge4Se10] (500), [CnHn+1NH3]Cl/EtOH, H2O, 60 °C 2 h	O286
(H24,4′-bipy)2[Ge4S10]·4,4′-bipy (539)	[Me4N]4[Ge4S10] (496), Cu(NO3)2, 4,4′-bipy/140 °C, 3 days	O287
[(CnH2n+1)2Vio]2[Ge4S10] (540–543, n = 0, 2, 3,4)	[Me4N]2[Ge4S10] (496), [(CnH2n+1)2Vio]/iPrOH, H2O, 3 days	O288
[Me2Vio]2[Ge4S10] (544)	[Me4N]2[Ge4S10] (496), [MV]I2/H2O, MeOH, DMF	O289
TMPyP[Ge4S10] (545)	[Me4N]2[Ge4S10] (496), TMPyP(PF6)4/MeOH, H2O, DMF, 80 °C, 7 days	O290
[DMBPE]2[Ge4S10] (546)	[Me4N]2[Ge4S10] (496), [DMBPE]I2/H2O	O291
[Ni(cyclam)]3[Ni(cyclam)(H2O)2][Ge4S10]2 (547)	[Me4N]2[Ge4S10] (496), [Ni(cyclam)](ClO4)2/MeCN, H2O, 3 days	O292
[Mn(2,2′-bipy)2H2O][Ge4S10] (548)	[Me4N]2[Ge4S10] (496), [Mn(2,2′bipy)3](ClO4)2/MeCN, H2O, 3 days	O292
[Fe(2,2′-bipy)3]2[Ge4S10] (549)	[Me4N]2[Ge4S10] (496), [Fe(2,2′bipy)3](ClO4)2/H2O, 1 day	O292
[Ni(phen)3]2[Ge4S10] (550)	[Me4N]2[Ge4S10] (496), [Ni(phen)3]Cl2/MeOH, H2O, 12 h	O293
MnTMPyP[Ge4S10] (551)	[Me4N]2[Ge4S10] (496), TMPyP(PF6)4, MnCl2/MeOH, H2O, DMF, 80 °C, 7 days	O290
[Ni(trien)2]2[Ge4S10] (552)	GeO2, NiCl2, S/trien, 160 °C, 5 days	B294
[M(dap)3]4[Ge4S10]Cl4 (553–554, M = Co, Ni))	GeO2, Sb, S, MCl2/dap, 170 °C, 6 days	B295
[Ni2(μ-teta)(teta)2][Ge4S10] (555)	GeO2, S, NiCl2, teta/H2O, 170 °C, 12 days	B296,297
[Ni(teta)2]2[Ge4Se10] (556)	GeO2, Se, NiCl2, teta/H2O, 170 °C, 16 days	B296
[Ho2(tepa)2(OH)2Cl2]2[Sn4Se10] (557)	SnCl4·H2O, Se, HoCl3/tepa,170 °C, 6 days	B298
[Ni(teta)(en)][Ni(teta)(hda)][Sn4Se10] (558)	Sn, Se, Ni(OAc)2, hda/teta, 170 °C, 5 days	B299
[Ln2(tepa)2(OH)2Cl2]2[Sn4Se10] (559–562, Ln = Y, Dy, Er, Tm)	SnCl4·5H2O, Se, LnCl3, Ag/tepa, 180 °C, 6 days	B300
[(Me)2NH2]6[Ge2Sb2S7][Ge4S10] (563)	GeO2, Sb, S/DMF, 160 °C, 7 days	B301
[Mn(en)3]2[Ge4O6Te4] (564)	Ge, Te, Mn(OAC)2, [Me4N]I/en, 150 °C, 80 h	B302

^aVio = viologen dication, TMPyP = 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin, DMBPE = N,N′-dimethyl-1,2-bis(4-pyridinium)-ethylene, cyclam = 1,4,8,11-tetraazacyclotetradecane, trien = triethylentetramin, teta = triethylenetetramine.

Hybrid adamantane-type cluster compounds with group 14 elements in the Q position and group 16 atoms in the E position^a.

Compound	Reagents/conditions	Method
[(MeSi)4S6] (565)	MeSiCl3, H2S/200 °C, 12 h	F304,305
[(EtSi)4S6] (566)	EtSiCl3, H2S/150 °C, 3 h	F304
[(ThexSi)4S6] (567)	1. Li2S, ThexSiCl3/THF, 0 °C to RT, 14 days	D306,307
	2. Decaline, 195 °C, 24 h
[(PhSi)4S6] (568)	PhSiCl3, Na2S/THF, 0 °C to RT, 24 h	D310
[(RSi)4S6] (569–570, R = 1-Np, Sty)	Na2S, 1-NpSiCl3/THF, 0 °C, 18 h	D309
[(MeSi)4Se6] (571)	MeSiCl3, H2Se/400 °C, 1 h	F304
[(EtSi)4Se6] (572)	EtSiCl3, H2Se, Al/150 °C, 3 h	F304
[(ThexSi)4Se6] (573)	1. Li2S, ThexSiCl3/THF, 0 °C to RT, 5 days	D306,307
	2. Decaline, 150 °C, 3 h
[(PhSi)4Se6] (574)	Na2Se, PhSiCl3/THF, 0 °C, 18 h	D308
[(MeGe)4S6] (575)	MeGeBr3, H2S, NEt3/C6H6, 80 °C, 1 h	D311,312
[(EtGe)4S6] (576)	EtGeCl3, (SiH3)2S, Al2Cl6/CS2, 75 °C, 7 days	D313
[(CF3Ge)4S6] (577)	CF3GeCl3, (SiH3)2S, Al2Cl6/CS2, 80 °C, 10 days	D313
[(ThexGe)4S6] (578)	1. Li2S, ThexGeCl3/THF, 0 °C to RT, 24 h	D306,307
	2. Decaline, 195 °C, 24 h
[{HOOC(CH2)2Ge}4S6] (579)	HOOC(CH2)2GeCl3, Na2S/Me2CO, H2O, 3 h	D323
[{Me(O)CCH2CMe2Ge}4S6] (580)	MeOCCH2CMe2GeCl3, Na2S/Me2CO, H2O, 4 h	D323
[{NC(CH2)2Ge}4S6] (581)	NC(CH2)2GeCl3, Na2S/Me2CO, H2O, 5 h	D314
[(PhGe)4S6] (582)	PhGeCl3, Na2S/Me2CO, H2O, 1 h	D310
[(CF3Ge)4Se6] (583)	CF3GeCl3, (SiH3)2Se, Al2Cl6/n-hexane, 110 °C, 4 days	D313
[(ThexGe)4Se6] (584)	1. Li2Se, ThexGeCl3/THF, 0 °C to RT, 24 h	D306,307
	2.C6H6, 80 °C, 24 h
[{NC(CH2)2Ge}4Se6] (585)	NC(CH2)2GeCl3, Na2Se/THF, 30 h	D314
[(MeSn)4S6] (586)	MeSnI3, H2S, HCl/H2O or MeSnCl3, Na2S/Me2CO, H2O, 3 h	G/D303,304,315,316
[(PhSn)4S6] (587)	PhSnCl3, Na2S/Me2CO, H2O, 4 h	D304
[(nBuSn)4S6] (588)	n BuSnCl3, Na2S/Me2CO, H2O, 3 h	D304,316,317
[(nPrSn)4S6] (589)	(nPrSn)2O3, Na2S, HCl/H2O, 3 h	D316
[(mesSn)4S6] (590)	mesSnCl3, Na2S/H2O, Me2CO, 0 °C, 12 h	D319
[(1-NpSn)4S6] (591)	1-NpSnCl3, Na2S/H2O, Me2CO, 0 °C, 18 h	D319
[(4-MeC6H4Sn)4S6] (592)	4-MeC6H4SnCl3, Na2S/H2O, Me2CO, 0 °C, 4 h	D319
[(4-MeOC6H4Sn)4S6] (593)	4-MeOC6H4SnCl3, Na2S/H2O, Me2CO, 0 °C, 2 h	D319
[(4-FC6H4Sn)4S6] (594)	4-FC6H4SnCl3, Na2S/H2O, Me2CO, 0 °C, 14 h	D319
[(3-FC6H4Sn)4S6] (595)	3-FC6H4SnCl3, (SiMe3)2S/10 °C, 1 h	D319
[(C6F5Sn)4S6] (596)	C6F5SnCl3, (SiMe3)2S/C6H6, 10 °C, 15 min	D319
[{(Me3Si)3CSn}4S6] (597)	[(Me3Si)3CSnBr3], Na2S/NH3, 24 h	D317
[(StySn)4S6] (598)	PhSnCl3, Na2S/THF, 0 °C to RT, 24 h	D320
[(CySn)4S6] (599)	CySnCl3, (SiMe3)2S/toluene, 24 h	D321
[(BnSn)4S6] (600)	BnSnCl3, (SiMe3)2S/toluene, 5 min	D321
[{EtO2C(C6H4)CH2CH2Sn}4S6] (601)	EtO2C(C6H4)CH2CH2SnCl3, (SiMe3)2S/toluene, 2 h	D321
[(CpSn)4S6] (602)	1. SnCl4, NaCp/toluene, 0 °C, 5 h	D321
	2. (SiMe3)2S/toluene, 1 h
[(MeSn)4Se6] (603)	MeSnBr3, NaHSe, Na[BH4]/H2O, 1 h	D318
[(nBuSn)4Se6] (604)	Na2Se, nBuSnCl3/NH3, −33 °C, 5 h	D317
[{(Me3Si)3CSn}4Se6] (605)	[(Me3Si)3CSnBr3], Na2Se/NH3, 24 h	D317
[(iPrSn)4Se6] (606)	iPrSnCl3, Na2S/H2O, Me2CO, 0 °C, 18 h	D322
[(PhSn)4Se6] (607)	PhSnCl3, (SiMe3)2Se/toluene, 5 min	D321
[(BnSn)4Se6] (608)	BnSnCl3, (SiMe3)2Se/toluene, 5 min	D321
[EtO2C(C6H4)CH2CH2Sn)4Se6] (609)	EtO2C(C6H4)CH2CH2SnCl3, (SiMe3)2Se/toluene, 16 h	D321
[(CpSn)4Se6] (610)	1. SnCl4, NaCp/toluene, 0 °C, 5 h	D321
	2. (SiMe3)2S/toluene, 5 min
[(CySn)4Se6] (611)	CySnCl3, (SiMe3)2Se/toluene, 1 h	D321
[{Me(PhNHN)CCH2CMe2Ge}4S6] (612)	[(MeOCCH2CMe2Ge)4S6], H2NNHPh/CH2Cl2, 3 h	Q323
[(N(SiMe3)DippSi)4Te6] (613)	[Si4{N(SiMe3)Dipp}4], (nBu)3PTe/toluene, 110 °C, 2 h	J324
[{N(2,6-iPr2C6H3)(SiMe3)Sn}4E6] (614–615, E = S, Se)	N(2,6-iPr2C6H3)(SiMe3)SnCl, E/THF, 18 h	C325
[({Cp(CO)2Fe}Sn)4Se6] (616)	[{Cp(CO)2Fe}2SnCl2], (SiMe3)2Se/THF	D326
[({Cp(CO)3Mo}Sn)4Te6] (617)	[{Cp(CO)3Mo}SnCl3], (SiMe3)2Te/THF, −78 to −18 °C, 19 days	D327
[({Cp(CO)Fe}2Sn)4S6] (618)	[{Cp(CO)2Fe}SnCl3], (Bu3Sn)2S/toluene, 12 h	D328
[(FcSn)4S6] (619)	FcSnCl3, Na2S/THF, 0 °C, 31 h	D329
[(FcSn)4Se6] (620)	FcSnCl3, K2Se/THF, 48 h	D330
[{(PhSn)3SnS6}{(MCp)3S4}] (621–622, M = Mo, W)	[(PhSn)4S6] (587), [M(CO)3CpCl], (Me3Si)2S/THF, 15 h	R331
[Au(dppe)2][{Me(H2NN)CCH2CMe2Sn}4S6Cl] (623)	1. [{Me(O)CCH2CMe2Sn}3S4]Cl, AuCl, dppe, (Me3Si)2S,/CH2Cl2, 17 h	R332
	2. PhNHNH2/CH2Cl2, 45 min
[(μ4-O)Pb4(OSiPh3)6] (624)	Ph3SiOH, [Pbcp2]/Et2O, 35 °C, 30, min	D333,334
[(tBuSi)4O6] (625)	t BuSiCl3, H2O/Et2O, 24 h	I335
[(iPrSi)4O6] (626)	iPrSiCl3, H2O/Et2O, −80 °C to RT, 2 days	I335
[{(Me3Si)3CSn}4O6] (627)	[(Me3Si)3CSnBr3], Na2O/NH3, THF, −78 °C, 6 h	D317
[({Cp*(CO)2Ru}2Ge)4O6] (628)	1. [Cp*RuCO(GeCl2)]2, K/THF, 48 h	I336
	2. O2
[{(CO)5WGe}4O2(OH)4] (629)	1. 2-Methoxybenzyl alcohol, Ge[N(SiMe3)2]2/Et2O, 30 min	I337
	2. [W(CO)5(thf)]/THF, 12 h
	3. H2O in pentane
[(Sn(DMEGqu)Br)4O4(OH)2]Br2 (630)	SnBr4, 3,5-ditert-butyl-o-benzoquinone, DMEGqu/THF, H2O	I338

^aThex = 1,1,2-trimethylpropyl, Np = naphthyl, Sty = para-styryl, Cy = cyclohexyl, Cp = cyclopentadienyl, Dipp = 2,6-diisopropylphenyl, DMEGqu = N-(1,3-dimethylimidazolidin2-ylidene)quinoline-8-amine.

Adamantane-type with group 15 and lanthanide elements in Q position and group 16 atoms in the E position^a.

Compound	Reagents/conditions	Method
[P4O7] (631)	P4O6, H2O/diglyme, 140 °C	P339–342
[(P4O6Sx] (632–635, x = 1–4)	P4O6, [P4S10]/PhMe, 110 °C	P343
[(SP)4O6] (635)	P4O6, S/160 °C	P345–347
[(P4O6Sex] (636–638, x = 1–3)	P4O6, [P4Se10]/PhMe, 110 °C	P343,344
[(P4O6SSe] (639)	[P4O6S] (632), [P4Se10]/PhMe, 110 °C	P343
[P4O7Sx] (640–642, x = 1–3)	[P4O7] (631), [P4S10]/PhMe, 110 °C	P343,348
[P4O7Se] (643)	[P4O7] (631), [P4Se10]/PhMe, 110 °C	P343,349
[P4O8] (644)	[P4O7] (631), [P4S10]/PhMe, 110 °C	P343
[P4O8Sx] (645–646, x = 1–2)	[P4O7] (631), [P4S10]/PhMe, 110 °C	P343
[P4O6{Ni(CO)3}x] (647–650, x = 1–4)	P4O6, Ni(CO)4/10 min	P350–352
[(P4O6)xNi(CO)4−x] (651–652, x = 2–3)	P4O6, Ni(CO)4/10 min	P350,351
[P4O6{Fe(CO)4}x] (653–656, x = 1–4)	P4O6, [Fe(CO)5]/103 °C, 24 h	P351,353
[P4S10] (657)	P, S,/100 °C	A354–356
[{(8-HQ)(p-X-C6H4)Sb}4O6] (658–659, X = Cl, Br)	p-X-C6H4SbO3H2, 8-HQ/toluene, 110 °C, 6 h	C357
[{(H2naphpz)(p-X-C6H4)Sb}4O6] (660–661, X = Cl, Br)	p-X-C6H4SbO3H2, H2naphpz/toluene, 110 °C, 6 h	C357
[{(dpan)(OH)Sb}4O6] (662)	dpanSbCl4, NaOH/H2O, Et2O, 18 h	I358
[(μ4-O){Ce(LOEt)}4O4(OH)2] (663)	[Et4N]OH, [CeLOEt(NO3)3]/MeCN, 1 h	C366
[(μ4-O){Ce(LOEt)}4(O2)4(OH)2] (664)	[(μ4-O){Ce(LOEt)}4O4(OH)2] (663), H2O2/MeCN, 1 h	I366
[(μ4-O){M(3-NO2Tp)}4(μ2-OMe)6] (665–666, M = Gd, Tb)	MCl3·H2O, [Bu4N][3-NO2Tp]/MeOH, 3 days	C367
[(μ4-O){M(3-NO2Tp)}4(μ2-OMe)6] (667–670, M = Pr, Nd, Sm, Eu)	MCl3·H2O, [Bu4N][3-NO2Tp]/MeOH, 2–4 weeks	C367
[(μ4-O){(SON)Yb}4(SON)4(OH)2] (671)	Yb[N(SiMe3)2], HBT/DME, H2O, 30 °C, 1 h	I/K368
[(μ4-O)M4(HL)3(SCN)4(H2O)2] (672–673, M = Dy, Eu)	H3L, Et3N, M(SCN)3·6H2O/MeOH, MeCN, 100 °C, 2 days	K369

^a8-HQ = 8-hydroxyquinoline, H₂naphpz = 2-[1H-pyrazol-5(3)-yl]naphthalene-1-ol, dpan = 6-diphenylphosphinoacenaphth-5-yl, L_OEt = [Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]⁻, 3-NO₂Tp = 3-nitrotrispyrazolylborate, SON = (benzothiazole-2-yl)phenolate, HBT = 2-(2-hydroxyphenyl)benzothiazole, H₃L = 2-hydroxy-N-[2-hydroxy-3-[(2hydroxybenzoyl)amino]propyl]benzamide.

Adamantane-type clusters with group 2 and 4–8 atoms in Q position and group 17 atoms in E position^a.

Compound	Reagents/conditions	Method
[H4N]2[Be4Cl10] (674)	BeCl2, NH4Cl/400–230 °C	A370
Cs2[Be4Cl10] (675)	BeCl2, CsCl/400–230 °C	A370
Rb2[Be4Cl10] (676)	BeCl2, RbCl/400–230 °C	A370
K2[Be4Cl10] (677)	BeCl2, KCl/400–230 °C	A370
Tl2[Be4Cl10] (678)	BeCl2, TlCl/400–230 °C	A370
[μ4-O{Mg(Et2O)}4Br6] (679)	BrMgPh, O2/Et2O	G371,372
[TiF2(15-crown-5)][(TiF3)4F6] (680)	TiF4, 15-crown-5/MeCN	C373
[o-C6H4(PPh2H)2][(TiF3)4F6] (681)	TiF4, o-C6H4(PPh2)2/MeCN, CH2Cl2, 1 h	C374
[o-C6H4(AsMe2H)2][(TiF3)4F6] (682)	TiF4, o-C6H4(AsMe2)2/MeCN, CH2Cl2, 1 h	C374
[HiPrS(CH2)2SiPrH][(TiF3)4F6] (683)	TiF4, iPrS(CH2)2SiPr/MeCN, CH2Cl2, 1 h	C374
[Me4N]2[(TiF3)4F6] (684)	TiF4, [Me4N]F/HF, −196 K to RT	F375
[Ph4P]2[(TiF3)4F6] (685)	TiF4, [Ph4P]F/HF, −196 K to RT	F375
[(TiCl3)2(Ti2{da6aH2(H2)})F6] (686)	TiF4, p-methyl-dimethyldiazacalix[6]areneH6/toluene, 110 °C	C376
[C4mim]2[(TiCl3)4F6] (687)	TiCl4, [C4mim][BF4]/70 °C	B377
[{Nb)NMe2)3}4F6]Cl2 (688)	NbF5, Me3SiNMe2/toluene, CHCl3	C378
[{Nb)NMe2)3}4F6]Br2 (689)	[{Nb(NMe2)3}4F6]Cl2 (688)/CH2Br2	O378
[{Nb)NMe2)3}4{Nb)NMe2)2}F5O]Cl2 (690)	[{Nb(NMe2)3}4F6]Cl2 (688)/H2O	I378
[μ4-O{Cr(thf)}4Cl6] (691)	LiOH·H2O, nBuLi, CrCl2/THF, hexane	C379
[μ4-O{Cr(thf)}4Cl4I2] (692)	[Cr3Cl3(μ-Cl)3(μ3-CH)(thf)6], benzaldehyde/THF	J380
[μ4-O{Cr(thp)}4Cl4I2] (693)	CrCl2, CHI3/THP, −35 °C to RT, 19 h	C380
[Cp2WCl2]2[(WF3)4F6] (694)	[Cp2WCl2], WF6/SO2	C381
[μ4-O{Mn(PnPr3)}4Cl6] (695)	[MnI2(PnPr3)], O2/n-pentane	F382
[μ4-O{Mn(PnPhMe2)}4Cl6] (696)	[MnI2(PnPhMe2)], O2/n-pentane	F383
[H8-HQ]6[(FeF3)4F6] (697)	FeF2, FeF3, 8-HQ, HF/H2O, EtOH, 120 °C, 72 h	B384

^aC₄mim = 1-butyl-3-methylimidazolium, da6aH₆ = p-methyl-dimethyldiazacalix[6]areneH₆.

Adamantane-type clusters with a central μ₄-oxygen atom, Cu in the Q position and group 17 atoms in the E position^a.

Compound	Reagents/conditions	Method
[μ4-O{Cu(Py)}4Cl6] (698)	CuCl2, NaOH/Py, 2 days	C385
[μ4-O{Cu(2-methylpyridine)}4Cl6] (699)	CuCl2, 2-methylpyridine/MeOH, 65 °C, 24 h	C387
[μ4-O{Cu(OPPh3)}4Cl6] (700)	CuCl2, CuO, OPPh3/MeNO2, 100 °C, 3 h	C386
[μ4-O{Cu(3-quinuclidinone)}4Cl6] (701)	CuCl2·2H2O, 3-quinuclidinone, MeONa/MeOH, 65 °C, 15 min	C388
[μ4-O{Cu(HMTA)}4Cl6] (702)	CuCl2·H2O, HMTA/Me2CO	C389
[μ4-O{Cu(OSR2)}4Cl6] (703–704, R = Et, nPr)	CuCl2·2H2O, OSR2/Me2CO, 24 h	C390
[μ4-O{Cu(N-Methylimidazole)}4Cl6] (705)	CuCl2·2H2O, N-methylimidazole/MeOH	C391,392
[μ4-O{Cu(dmso)}4Cl6] (706)	Cu/CCl4, DMSO	C393,394
[μ4-O{Cu(MeCN)}4Cl6] (707)	CuCl2·2H2O, HBDA/MeCN, 82 °C	C394,395
[μ4-O{Cu(1,2-dimethylimidazole)}4Cl6] (708)	CuCl2·2H2O, 1,2-dimethylimidazole/EtOH, MeOH	C396
[μ4-O{Cu(nictonie)}4Cl6] (709)	CuCl2·2H2O, nicotine/H2O, Me2CO	C397
[μ4-O{Cu(3,4-dimethyl-5-phenylpyrazole)}4Cl6] (710)	CuCl2·2H2O, 3,4-dimethyl-5-phenylpyrazole/EtOH	C398
[μ4-O{Cu(N,N-dimethylaminomethylferrocene)}4Cl6] (711)	CuCl, N,N-dimethylaminomethylferrocene, O2/CH2Cl2, 20 min	C399
[μ4-O{Cu(7-azaindol)}4Cl6] (712)	CuCl2·2H2O, 7-azaindol/MeOH, 65 °C, 15 min	C400
[μ4-O{Cu(Me2NH)}4Cl6] (713)	Cu/Me2NH·HCl, DMF, 50 °C, 30 min	C401
[μ4-O{Cu(cpz)}4Cl6] (714)	CuCl2·2H2O, cpz/EtOH	C402
[μ4-O{Cu(1-(4-picolylpyrrolidin-2-on)}4Cl6] (715)	CuCl2·2H2O, 1-(4-picolyl)pyrrolidin-2-on/MeOH	C403
[μ4-O{Cu(morpholine)}4Cl6] (716)	CuCl, morpholine, Cl3CCOOMe/MeCN, H2O, 30 min	C404,405
[μ4-O{Cu(Ph2SNH)}4Cl6] (717)	CuCl2·2H2O, Ph2SNH, air/MeCN, 1 day	C406
[μ4-O{Cu(Imidazole)}4Cl6] (718)	CuCl2·2H2O, imidazole/MeOH	C407
[μ4-O{Cu(thf)}4Cl6] (729)	CuCl2·2H2O/THF	C408
[μ4-O{Cu(2-methyl-2-thiazoline)}4Cl6] (720)	CuCl2·2H2O, 2-methyl-2-thiazoline/MeOH	C409
[μ4-O{Cu(2-ethylpyrazine)}4Cl6] (721)	CuCl, 2-ethylpyrazine, air/MeCN, 2 days	C410
[μ4-O(Cu{1-(1-Isoquinolyl)benzotriazole})4Cl6] (722)	CuCl2·2H2O, 1-(1-isoquinolyl)benzotriazole/MeOH, CHCl3, 1 day	C411
[μ4-O{Cu(3-mesitylpyrazole)}4Cl6] (723)	CuCl2·2H2O, 3-mesitylpyrazole, NaOH/MeOH, 18 h	C412
[μ4-O{Cu(3-benzyl-benzimidazole)}4Cl6] (724)	CuSO4·5H2O, benzimidazole, benzlychloride/Py, 120 °C, 36 h	B413
[μ4-O{Cu(2-ethyltetrazole)}4Cl6] (725)	CuCl2·2H2O, 2-ethyltetrazole/MeOH, 1 h	C414
[μ4-O{Cu(1-Methylbenzotriazole)}4Cl6] (726)	CuCl2·2H2O, 1-methylbenzotriazole, CuO/MeOH, 65 °C, 1 h	C415
[μ4-O{Cu(pyridine N-oxide)}4Cl6] (727)	CuCl2·2H2O, pyridine N-oxide/MeOH, 45 min	C416
[μ4-O{Cu(2-Methylimidazole)}4Cl6] (728)	CuCl2·2H2O, 2-methylimidazole/MeOH, 45 min	C416
[μ4-O(Cu{OP(NHtBu)3})4Cl6] (729)	CuCl2·2H2O, OP(NHtBu)3/hexane, 80 °C, 38 h	C417
[μ4-O{Cu(3,5-dimethylpyrazole)}4Cl6] (730)	CuCl2·2H2O, acetylacetone, benzohydrazide/EtOH, 8 h	C418,419
[μ4-O{Cu(1,4-dioxane)}4Cl6] (731)	CuCl2·2H2O, 1,4-dioxane, benzoylhydrazine/MeOH, CH2Cl2, 30 min	C420
[μ4-O{Cu(1-ethyl-5-nitro-1,2,3-triazole)}4Cl6] (732)	CuCl2·2H2O, 1-ethyl-5-nitro-1,2,3-triazole/EtOH, 78 °C, 1 h	C421
[μ4-O{Cu(3-hydroxyethylpyridine)}4Cl6] (733)	CuCl2·2H2O, 3-hydroxyethylpyridine/MeOH	C422
[μ4-O{Cu(Quinuclidine)}4Cl6] (734)	CuCl, quinuclidine, air/MeCN, 82 °C, 30 min	C423
[μ4-O(Cu{1-(pyridin-2-ylmethyl)-1H-benzimidazole})4Cl6] (735)	CuCl2·6H2O, 1-(pyridin-2-ylmethyl)-1H-benzimidazole, air/MeCN, H2O	C424
[μ4-O{Cu(benzylamine)}4Cl6][Cu(benzylamine)2Cl2] (736)	CuCl2·2H2O, benzylamine/MeOH, 10 min	C394
[μ4-O{Cu(MeOH)}4Cl6] (737)	CuCl2·2H2O, CuO/MeOH, 65 °C, 2 h	C394
[μ4-O{Cu(PziPr2H)}4Cl6] (738)	CuCl2·2H2O, PziPr2H, sodium parafluorobenzoate/MeOH, 4 h	C425
[μ4-O{Cu(DASO)}4Cl6] (739)	CuCl, DASO, air/allyl chloride, 3 h	C426
[μ4-O{Cu(4-dimethylaminopyridine)}4Cl6] (740)	CuCl2·2H2O, 4-dimethylaminopyridine, 2,2,6,6-tetramethylpiperidinyl-1-oxyl, BnOH/MeOH, CH2Cl2, 10 min	C427
[μ4-O{Cu(phenethylamine)}4Cl6]·[Cu(phenethylamine)2Cl2] (741)	CuCl2·2H2O, phenethylamine/MeOH, 10 min	C428
[μ4-O{Cu(N,N-dimethylbenzylamine)}4Cl6] (742)	CuCl2·2H2O, N,N-dimethylbenzylamine/MeOH, 10 min	C428
[μ4-O{Cu(cyclohexanemethylamine)}4Cl6]·1,5[Cu(cyclohexanemethylamine)2Cl2] (743)	CuCl2·2H2O, cyclohexanemethylamine/MeOH, 10 min	C428
[μ4-O{Cu(pyrazole)}4Cl6] (744)	CuCl2·2H2O, pyrazole/MeOH, 65 °C, 2 h	C455
[μ4-O{Cu(dimethyl acetamide)}4Cl6] (745)	CuCl2·2H2O, dimethyl acetamide/1,4-dioxane, 50 °C, 24 h	C429
[μ4-O{Cu(1-vinylimidazole)}4Cl6] (746)	CuCl2·2H2O, 1-vinylimidazole/MeOH, H2O, 60 °C, 2 days	C430
[μ4-O{Cu(metronidazole)}4Cl6] (747)	CuCl, metronidazole, air/MeOH	C431
[μ4-O{Cu(NCNMe2)}4Cl6] (748)	CuCl2·2H2O/NCNMe2	C432
[μ4-O{Cu(4-(phenylethynyl)pyridine)}4Cl6] (749)	CuCl, 4-(phenylethynyl)pyridine, air/CH2Cl2, 24 h	C433
[μ4-O{Cu(pyridine-3-carbaldehyde)}4Cl6] (750)	CuCl2·2H2O, pyridine-3-carbaldehyde/MeOH, CH2Cl2, 70 °C, 6 days	B434
[μ4-O{Cu(2-ethylpyridine)}4Cl6] (751)	CuCl2·2H2O, 2-ethylpyridine, air/MeOH, 50 °C, 1 h	C435
[μ4-O(Cu{N-(α-4-picolyl)piperidine})4Cl6] (752)	CuCl2·2H2O, N-(α-4-picolyl)piperidine/MeCN	C436
[μ4-O{Cu(OPEt3)}4Cl6] (753)	[PEt3CuCl]4/CCl4, CH2Cl2, 4 days	C437
[μ4-O{Cu(DENC)}4Cl6] (754)	[{(DENC)CuCl}4O2]/MeOH, CH2Cl2	J438
[μ4-O{Cu(benzimidazol)}4Cl6] (755)	[Cu2Cl3(benzimidazol)5]Cl/EtOH	J439
[μ4-O{Cu(dmf)}4Cl6] (756)	[μ4-O{Cu(MeOH)}4Cl6] (737)/DMF	Q394
[μ4-O{Cu(3-nonyl-8-fluoroimidazo[1,5-a]pyridine)}4Cl6] (757)	[μ4-O{Cu(MeCN)}4Cl6] (707), 3-nonyl-8-fluoroimidazo[1,5-a]pyridine/MeCN, 100 °C, 10 min	Q440
[μ4-O{Cu(Amt)}4Cl6] (758)	[Cu(α-CgPAmtHMe)(Cl)][BF4], KHMDS/THF	J441
[μ4-O{Cu(nmp)}3(CuOH2)Cl6] (759)	CuCl, O2/nmp, H2O	F442
[μ4-O{Cu(Me2NH)}3{Cu(dmso)}Cl6] (760)	Cu/Me2NH·HCl, DMSO, 50 °C, 2 h	C401
[μ4-O{Cu(Me2NH)}2{Cu(MeOH)}2Cl6] (761)	Cu/Me2NH·HCl, MeOH, 50 °C, 30 min	C401
[μ4-O{Cu(thf)}3(CuOH2)Cl6]2[μ4-O{Cu(thf)}4Cl6]2 (762)	CuCl2·2H2O, tetra-μ-acetato-κ8O:Ot-dicopper(ii) dehydrate/THF, 24 h	C443
[μ4-O{Cu(urea)}3{Cu(thf)}Cl6] (763)	[μ4-O{Cu(MeOH)}4Cl6] (737), urea/THF, 2 h	Q444
[4-phenylimidazolium][μ4-O{Cu(4-phenylimidazole)}3{CuCl}Cl6] (764)	CuCl2·2H2O, 4-phenylimidazole/MeOH, 45 min	C416
[μ4-O(Cu{N-(α-4-picolyl)morpholine})2(Cu{N-(α-4-picolyl)morpholinium})(CuCl)Cl6] (765)	CuCl2·2H2O, N-(α-4-picolyl)morpholine/MeCN, H2O	C436
[Me4N]4[μ4-O(CuCl)4Cl6] (766)	CuCl2, CuO, [Me4N]Cl/MeOH, 65 °C, 24 h	C445
[teedH2]2[μ4-O(CuCl)4Cl6] (767)	CuCl2, teed/EtOH	C446
[Et2NH2]4[μ4-O(CuCl)4Cl6] (768)	CuCl2, [Et2NH2]Cl/MeOH, 65 °C, 24 h	C447
(C11H24C12N4O2)2[μ4-O(CuCl)4Cl6] (769)	CuCl2, N,N′-bis[2-(dimethylamino)-ethyl]propanediamide/CHCl3, H2O	C448
[BMIm]4[μ4-O(CuCl)4Cl6] (770)	CuCl2·2H2O, [BMIm]Cl, O2, 2,3,6-trimethylphenol/nBuOH, 60 °C	C449
[H2BPBACy]2[μ4-O(CuCl)4Cl6] (771)	CuCl2·2H2O, BPBACy/MeNO2, MeOH	C450
[choline]4[μ4-O(CuCl)4Cl6] (772)	CuCl2·2H2O, air/choline chloride	C451
[μ4-O{Cu(Py)}4Br6] (773)	CuBr2, CuO, Py/H2O, 100 °C	C452
[μ4-O{Cu(nicotine)}4Br6] (774)	CuBr, 4-cyanopyridine, nicotine/DMF, 40 min	C458
[μ4-O{Cu(2-bromo-1-methyl-imidazole)}4Br6] (775)	CuBr, 2-mercapto-1-methyl-imidazoline, air/MeCN, CHCl3	C453
[μ4-O{Cu(clotrimazole)}4Br6] (776)	CuBr2, clotrimazole/EtOH, 78 °C, 4 h	C454
[μ4-O{Cu(benzylamine)}4Br6][Cu(benzylamine)2Br2] (777)	CuBr2, benzylamine/MeOH, 10 min	C394
[μ4-O{Cu(3,5-dimethyl-4-bromo-pyrazole)}4Br6] (778)	CuBr2, acetylacetone, benzohydrazide/EtOH, 8 h	C455
[μ4-O{Cu(NCNMe2)}4Br6] (779)	CuBr2/NCNMe2	C432
[μ4-O{Cu(MeOH)}4Cl6−nBrn] (780–786)	CuCl2·2H2O, CuBr2, CuO/MeOH, 60 °C, 4 h	C456
[μ4-O{Cu(morpholine)}4Cl6−nBrn] (787–793, n = 0–6)	[μ4-O{Cu(MeOH)}4Cl6−nBrn] (780–786), morpholine/MeOH, 60 °C, 6 h	Q456
[μ4-O{Cu(piperidine)}4Cl6−nBrn] (794–800, n = 0–6)	[μ4-O{Cu(MeOH)}4Cl6−nBrn] (780–786), piperidine/MeOH, 60 °C, 6 h	Q456
[μ4-O{Cu(OPPh3)}4Cl6−nBrn] (801–807, n = 0–6)	[μ4-O{Cu(MeOH)}4Cl6−nBrn] (780–786), OPPh3/MeOH, 60 °C, 6 h	Q456,457

^aHMTA = hexamethylentetramine, HBDA = hexakis(trimethylsilyl)benzdiamidine, cpz = 2-chloro-10-(3-dimethylaminopropyl(phenothiazine), DENC = N,N-diethylnicotinamide, Pz^iPr2H = 3,5-diisopropylpyrazole, DASO = diallyl sulfoxide, Amt = 1,3-diamino-1,2,2-trimethylcyclopentane, CgP = 1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphatricyclo[3.3.1.1]-decane, nmp = N-methyl-2-pyrrolidinone, teed = N,N,N′,N′-tetraethylethylenediamine, BPBACy = bis(1-propylbenzimidazol-2-yl)-trans-1,2-cyclohexane.

Adamantane-type clusters without a central μ₄-oxygen atom, group 11–13 elements in the Q position and group 17 atoms in the E position^a.

Compound	Reagents/conditions	Method
[H2dpipa]3[Cu4Cl6][Cu2Cl6] (808)	Cu, dpipa, HCl/H2O, 180 °C, 24 h	B459
[iPr4N]2[Cu4Br6] (809)	CuBr, [iPr4N]Br,/EtOH	C460,461
[nBuNPh3]2[Cu4Br6] (810)	CuBr, [nBuNPh3]Br/EtOH	C462
[N(PPh3)2]2[Cu4Br6] (811)	CuBr, [N(PPh3)2]Br/EtOH, heat	C463
[tBu3NMe]2[Cu4Br6] (812)	CuBr, [nBu3NMe]Br/iPrOH, 100 °C, 30 min	C461
[Mg(thf)6][Cu4Br6] (813)	CuBr, MgBr2/THF, 50 °C, 18 h	C464
[(Poxim)2AlBr][Cu4Br6] (814)	[Al(C6F5)3(toluene)0.5], CuOtBu, poxim, allyl bromide, C14H30/toluene, −30 °C to 80 °C, 7 h	U465
(H2dpipa)3[Cu4Br6][Cu2Br6] (815)	Cu, HBr, dpipa/180 °C, 24 h	B459,467
[Ti12(μ3-O)14(OiPr)18][Cu4Br6] (816)	CuBr, [Ti(OiPr)4]/iPrOH, 80 °C, 3 days	B466
[{Cu(Hdabco)}4Br6](HCOO)2 (817)	CuBr, dabco/DMF, H2O, 85 °C, 72 h	C468
[MePPh3]2[Cu4I6] (818)	CuI, [MePPh3]I CuI/MeNO2, EtOH, heat	C469,470
[MeAsPh3]2[Cu4I6] (819)	CuI, [MePPh3]I/MeNO2, EtOH, heat	C469
[Ph4P]2[Cu4I6] (820)	Cu, I2, [Ph4P]I/Me2CO, 56 °C	C471
[(C7H16)4N]2[Cu4I6] (821)	Cu, I2, [(C7H16)4N]/hydroxyacetone, heat	C472
[O{P(pyr)3}2][Cu4I6] (822)	CuI, KI, ClP(pyr)3/MeCN, 90 °C, 1 day	B473
[KN{(CH2)2O(CH2)2OMe}3]2[Cu4I6] (823)	CuI, KI, N{(CH2)2O(CH2)2OMe}3	C474
[Li(benzo-15-crown-5)H2O]2(benzo-15-crown-5)[Cu4I6] (824)	CuI, LiI, benzo-15-crown-5, ascorbic acid/H2O, Me2CO, reflux, 4 h	C475
[Cs(benzo-15-crown-5)]2[Cu4I6] (825)	CuI, CsI, benzo-15-crown-5, ascorbic acid/H2O, Me2CO, reflux, 2 h	C475
[Na(18-crown-6)H2O]2(H2O)[Cu4I6] (826)	CuI, NaI, 18-crown-6, ascorbic acid/H2O, Me2CO, reflux, 6 h	C475
[Rb(18-crown-6)]2(MeCN)[Cu4I6] (827)	RbI, Cu, [NH4]I, 18-crown-6/MeCN, 60 °C, 28 h	C476
[Mn(tdpmO3)2][Cu4I6] (828)	CuI, MnI2, tdpmO3/MeCN, 30 min	C477
[Mn(dppbO2)3]2[Cu4I6][Cu2I4] (829)	CuI, MnI2, dppbO2/MeCN, 1 h	C477
(BPPIP)[{(BPPIP)Cu2I3}2][Cu4I6] (830)	(BPPIP)I, CuI/CH2Cl2, MeOH	C478
K[K(12-crown-4)]6[Cu4I6][Cu8I13] (831)	CuI, KI, 12-crown-4/H2O, Me2CO	C479
[Co(tib)2][Cu4I6] (832)	CoO, CuI, tib, KI, HI/MeOH, 145 °C, 7 days	B480
[{Cp*NbClO}3][(Cp*Nb)3Cl2O3OH][(ZnCl)4Cl6] (833)	[(Cp*NbCl2)2ClO(OH], Zn, ZnO/CH2Cl2	U481
[(Cp*TaCl)3O3(OH)2][(ZnCl)4Cl6] (834)	[(Cp*TaCl2)2Cl2O] Zn, O2/CH2Cl2	U482
[H3dien]2[Al4F18] (835)	Al(OH)3, dien, HF/EtOH, 190 °C microwave heating, 1 h	B483
[H3tren]2[Al4F18]·3.5H2O (836)	Al(OH)3, tren, HF/EtOH, 190 °C microwave heating, 1 h	B484
(H3O)2[Hgua]16[Al4F18]3 H2O (837)	Al(OH)3, HguaCl, HF/EtOH, 190 °C microwave heating, 1 h	B485

^adpipa = N,N′-dimethylpiperazine, PoxIm = N-phenyl-N′-{bis(tertbutyl)phosphinoxide}-imidazolylidene, dabco = 1,4-diazabicyclo[2.2.2]octane, tib = 1,3,5-tris(1-imidazolyl)benzene, pyr = pyrrolidine, dppbO₂ = 1,2-bis(diephenlyphospineoxide) benzol, tdpmO₃ = tris(diephenlyphospineoxide) methan, BPPIP = bis-triphenylphosphonio-isophosphindolide, THP = tetrahydropyran, tren = tris(2-ethylamino)amine, gua = guanidine.

Adamantane-type cluster with transition metal atoms in the E position^a.

Compound	Reagents/conditions	Method
[nBu4N]2[(PSiMe3)4(ZnI)6(thf)2] (838)	[ZnI2{P(SiMe3)3}]2, [nBu4N]2I/THF, 24 h	J486
[nBu4P]2[(AsSiMe3)4(ZnI)6(thf)2] (839)	[ZnI2{As(SiMe3)3}]2, [nBu4P]2I/THF, 24 h	J487
[(Pd{(η3-C3H5)}4(OH)6]CF3SO3 (840)	[(Bdpman)Pd(η3-C3H5)]CF3SO3/H2O, pentane	I488
[{Cu(bme*daco)}2(CuCl)4] (841)	(bme*daco)Cu, CuCl/MeCN	K489
[(4-SC5H4NH)4(CuCl)6] (842)	CuCl2 HS-4-C5H4N, KI/EtOH, 160 °C, 60 h	B490
[(4-SC5H4NH)4(CuBr)6] (843)	CuBr, 4,4′-bipyridyldisulfide/EtOH, 120 °C, 3 days	B491
[Cu6(phen)4(SPh)4Cl2] (844–845)	PhSH, phen, CuOtBu/THF, CH2Cl2, 18 h	C492
[(NEt4]4[(SPh)4(CuX)6] (846–847, X = Cl, Br)	[CuSPh]n, [NEt3]X/DMF, 10 min	J170
[(SePh)4Cu6{(Ph2P)2R}4][BF4]2 (848–849, R CH2, NH)	HSePh, NEt3 [Cu2{(Ph2P)2R}2(MeCN)2][BF4]2/THF, Me2CO, 12 h	J493
[(ER)4Ag6{(Ph2P)2Me}4][PF6]2 (850–853, ER = SPh, SC6H4Me-p, SePh, SeC6H4Cl-p)	NaER, [Ag2{(Ph2P)2Me}2(MeCN)2][PF6]2/CH2Cl2, 12 h	J494
[(SC6H4(NH2)-m)4Ag6{(Ph2P)2NH}4][BF4]2 (854)	NaSC6H4(NH2)-m, [Ag2{(Ph2P)2MNH}2][BF4]2/MeCN, CH2Cl2 12 h	J495
[(SC6H4Me-p)4Ag6{(Ph2P)2Me}4][PF6]2 (855)	[AgSC6H4Me-p]n, dppm, [NH4][PF6]/CH2Cl2, 4 h	J496
[(SR)4Ag6{(Ph2P)2Me}4][ClO4]2 (856–857, R C6H4Me-p, 2-Np)	[AgSR]n, dppm, LiClO4/CH2Cl2, 3 h	J496
[NMe4]5[(μ4-Mo)S4(CuCI)3(CuCI2)3] (858)	[NMe4]2[MoS4], CuCl/MeCN, 1 h	C497
[O4(anpy)8Zn6(ZnEt)4] (859)	ZnEt2, anpy,/H2O	I/K498

^abme*daco = bis(N,N′-2-mercapto-2-methylpropyl)1,5-diazocyclooctane, bdpman = N,N′-bis(diphenylmethyl)-3,7-diazabicyclo[3.3.1]nonane.

Adamantane-type clusters with elements from different groups in equivalent positions^a.

Compound	Reagents/conditions	Method
[S4(CH2)2(BH2)4] (860)	THF-BH3,/CS2, 50 °C, 3 h	G499
[S4(CH2)(BH2)5] (861)	NaB3H8/CS2, 75 °C, 5 h	B500
[(MCl)2(MPnPr3)2(PPh2)4Cl2] (862–863, M = Zn, Cd)	MCl2, PnPr3, Ph2PSiMe3/THF, 12 h	C501
	ZnCl2, , Ph2PSiMe3/THF, 12 h	C502
[nBu4N]2[(CdI)4{P(SiMe3)3}2I4] (867)	[CdI2{P(SiMe3)3}]2, [nBu4N]2I/THF, 24 h	J486
[{(thf)Mg}4{Si(SiMe2tBu)2}2Cl4] (868)	[(thf)2Mg{Si(SiMe3tBu)2}]2, tBuMgCl·2 MgCl2/THF, C6H6, 0 °C	J503
[μ4-O{(thf)2Ca}3MgPh3Br3] (869)	MgBr2, CuPh, Ca/THF, −78 °C to RT, 20 h	C504
[{(1-C{NDippCH2CH2N})2(CH2)2PhO}2Mg4Br4] (870)	[{1-C(NDippCH2CH2N)}2(CH2)2PhOLi2N(SiMe3)2], MgBr2/THF, 12 h	K505
[{(1-C{NDippCH2CH2N})2(CH2)2PhO}Mg2(Mg(thf)}2Br4] (871)	[{1-C(NDippCH2CH2N)}2(CH2)2PhOLi2N(SiMe3)2], MgBr2/THF, 12 h	K505
(872–876, R = Ph, CH2SiMe3, R′ = H, E = S; R = ph, R′ H, E = Se, Te; R = R′ = Me, E = Se)	, Na2E/Me2CO, H2O, 0 °C to RT, 18 h	K506
[(PhSn)2(Me3SiCH2Sn)2S4(CH2)2] (877)	[(PhSn)4S4(CH2)2] (872), [(Me3SiCH2Sn)4S4(CH2)2] (873)/CH2Cl2, 2 days	R506
[(PhSn)4S4−xSex(CH2)2] (878–881)	[(PhSn)4S4(CH2)2] (872), [(PhSn)4Se4(CH2)2] (874)/CH2Cl2	R506
[(PhSn)4Se4−xTex(CH2)2] (882–885)	[(PhSn)4Se4(CH2)2] (874), [(PhSn)4Te4(CH2)2] (875)/CH2Cl2	R506
[{(Me3Si)2CH2Sn}4O4(CMe2)2] (886)	{(Me3Si)2CH2SnCl2}2CMe2, NaOH/H2O, PhMe, 80 °C, 18 h	K507
[MeSi{CH2Sn(S)Ph}3] (887–888, E = S, Se)	PhSi(CH2SnPhI2)3, Na2S/Me2CO, MeOH, H2O	K508
[PhSi{CH2Sn(S)Ph}3] (889–891, E = S, Se, Te)	PhSi(CH2SnPhCl2)3, (SiMe3)2E/toluene, 24 h	K509
[As4(CH2)3O3] (892)	1. CH2(AsPhCH2AsPh3)2, HI/CH2Cl2	I510
	2. NH3, H2O/THF
[(Cp*Ru)3(tBuSi)H6] (893)	[(Cp*Ru)3H5], tBuSiH3/hexane, 5 min	C511
[μ4-O(AlMe){(thf)Cl2Zr}3(OMe)6] (894)	[μ4-O{(thf)Cl2Zr}4(OMe)6], AlMe3/THF, PhMe, 12 h	R512
[Me4N][(MSPh)n(M′SPh)4−n(SPh)6] (895–899, M/M′ = Fe/Co, Fe/Zn, Fe/Cd, Co/Zn, Co/Cd)	[Me4N][(MSPh)4(SPh)6], [Me4N][(M′SPh)4 (SPh)6]/MeCN	C148
[Me3NBn]2[(FeCl)3Cu(SiPr)6] (900)	[Me3NBn]2[(Fe2(SiPr)6], FeCl2, CuCl/THF, 2 days, 70 °C	K513
[Me3NBn]2[(FeCl)3Cu(SeiPr)6] (901)	[Me3NBn]2[(Fe2(SeiPr)6], FeCl2, CuCl/MeCN, 1 day, 70 °C	J514
[nPr3N(CH2)6NnPr3][(FeBr)3Cu(SePh)6] (902)	CuBr, Fe(OAc)2, PhSeSiMe3, [nPr3N(CH2)6NnPr3]Br2/MeCN	C515
[(μ3-Cu)(CdPPh3)(CuPPh3)3(TePh)3(μ3-TePh)3] (903)	NaTePh, CuCl, CdCl2, PPh3/THF, 2 h	C516
[(μ3-Ag)(CdPPh3)(AgPPh3)3(TePh)3(μ3-TePh)3] (904)	NaTePh, AgCl, CdCl2, PPh3/THF, 3 h	C516
[(μ3-Cu)(ZnPiPr3)(CuPiPr3)3(TePh)3(μ3-TePh)3] (905)	[(PiPr3)3(CuTePh)4], ZnEt2, PiPr3, PhTeSiMe3/nHep, EtOH, 2 h, 0 °C to RT	C517
[(μ3-Cu){Cu(PR3)3}3(GaMe)(SePh)3(μ3-SePh)3] ((906–907, R = Me, Et2iPr)	1. CuOAc, PR3, Me3SiSePh/THF	J174
	2. Me3SiSePh, [Me2GaSePh]n/THF
[(μ3-Cu){Cu(PEt3)3}3(GaMe)(SePh)3(μ3-SePh)3] (908)	[(PEt3)5(CuSePh)6], Me3SiSePh, [Me2GaSePh]n/THF	J174
[(μ3-Cu){Cu(PEt3)3}3(GaMe)(TePh)3(μ3-TePh)3] (909)	[(PEt3)5(CuTePh)6], Me3SiTePh, Me3Ga·OEt2/THF	J174
[(W(O)OiPr)2{Ti(OiPr)2}2(O)4(bdmap)2] (910)	[W(O)(OiPr)3(bdmap)], Hbdmap, Ti(OiPr)4/PhMe, H2O, HOiPr, 2 days, 110 °C to 0 °C	C/I122
[H3TAEA]2[InGe4S11(SH)2(OH)] (911)	In(NO3), GeO2, TAEA/(CH2OH)2, nBuNH2, (CH2SH)2, 170 °C, 5 days	B518
[{Ni(bme*daco)}2(CuCl)4] (912)	(bme*daco)Ni, CuCl/MeCN	K489

^aHbdmap = 1,3-bis-(dimethylamino)-propan-2-ol, ⁿHep = normal heptane, TAEA = tris(2-aminoethyl)amine.

Compounds with an extended adamantane-type structure^a.

Compound	Reagents/conditions	Method
[μ3-Cu(CuPEtPh2)3{Cu(PEtPh2)2}Cu(TePh)6] (913)	CuCl, PEtPh2, Te(Ph)SiMe3/THF:Et2O, RT	C519
[μ3-Cu(CuPEt3)3{Cu(PEt3)2}Cu(SePh)6] (914)	CuOAc, Et3P, PhSeSiMe3/toluene, RT, 12 h	C520
[μ3-Cu(CuPEt3)3{Cu(PEt3)2}Cu(TePh)6] (915)	CuOAc, Et3P, PhTeSiMe3/Et2O, 0 °C, 2 h	C520
[Ag4{Ag(PEt3)2}2(TenBu)6] (916)	n BuTeSiMe3, AgCl–PEt3/pentane, −40 °C	C521
[Cu4(CuPiPr3)3(SePh)7] (917)	CuOAc, iPr3P, PhSeSiMe3/THF, RT, 1 h	C520
[μ3-(RuPPh3)(RuPPh3)4S6] (918)	[Ru(PPH3)3Cl2], S(SiMe3)2/MeCN, 85 °C, 6.5 h	C152
[μ3-(FeCl)(MoPEt3)(FePEt3)3S6] (919)	[Mo(thf)3Cl3], S(SiMe3)2, [Fe(PEt3)2Cl2]/THF, 50 °C, 4 h	D522,523
[μ3-(FeCl)(VPEt3)(FePEt3)3S6] (920)	[V(thf)3Cl3], S(SiMe3)2, [Fe(PEt3)2Cl2]/THF, RT	D522
[μ3-(FeSPh)(VPEt3)(FePEt3)3S6] (921)	[μ3-(FeCl)(VPEt3)(FePEt3)3S6] (920), NaSPh/THF, MeCN, RT	Q523
[μ3-(FeSPh)(MoPEt3)(FePEt3)3S6] (922)	[μ3-(FeCl)(MoPEt3)(FePEt3)3S6] (919), NaSPh/THF, MeCN, RT, 30 min	Q523
[μ3-(FeSEt)(VPEt3)(FePEt3)3S6] (923)	[μ3-(FeCl)(VPEt3)(FePEt3)3S6] (920), NaSEt/THF, MeCN, RT	Q523
[μ3-(FeSEt)(MoPEt3)(FePEt3)3S6] (924)	[μ3-(FeCl)(MoPEt3)(FePEt3)3S6] (919), NaSEt/THF, MeCN, RT, 30 min	Q523
[μ3-(FeS-p-C6H4OMe)(MoPEt3)(FePEt3)3S6] (925)	[μ3-(FeCl)(MoPEt3)(FePEt3)3S6] (919), NaS-p-C6H4OMe/THF, MeCN, RT, 30 min	Q523
[μ3-(VPEt3)(FePEt3)3FeS6}2S] (926)	[μ3-(FeCl)(VPEt3)(FePEt3)3S6] (920), Li2S/MeCN, RT, overnight	Q524
[μ3-(HgSPh)(AgPPh3)3Hg(SPh)6}2S] (927)	Na, HgO, PhSH, [Ag(PPh3)2]NO3/MeOH, CHCl3, 3 h	C525
[H3tren]4[(Al4F17)2F]OH (928)	Al(OH)3, tren, HF/EtOH, 190 °C microwave heating, 1 h	B484
[{P4(NMe)6}2CuCl]2 (929)	[P4(NMe)6], CuCl/MeCN, 2 days	T526
[H2Ta(tdci)2]CI3 (930)	TaCl5, tdci/MeOH	J527
[H11Ta7O12(tdci)6] (931)	[H2Ta(tdci)2]CI3/H2O	I527
[Ni{Ni(chp)2MeOH}6]Cl2 (932)	Ni(OH)2, Hchp/130 °C	C528
{[C2H4NH3)3NH]}2·(H3O)·[Al7F30] (933)	Al2O3, HF, tris(2-aminoethyl)amine/EtOH, 200 °C, 96 h	B529
[Si7C16H36] (934)	SiMe4/700 °C	A530,531
[Et4N]3[Cu4Sb(Te7)(Te2)2Te] (935)	1. K2Te, Cu, Sb2Te3, Te/heat to melt	E532
	2. [Et4N]Br/en

^atdci = 1,3,5-trideoxy-1,2,5-tris(dimethylamino)-cis-inositol, Hchp = 6-chloro-2-hydroxypyridine.

Networks of type 2 supertetrahedra^a.

Compound	Reagents/conditions	Method
[{P4(NMe)6}CuI]n (936)	[P4(NMe)6] (131), CuI/MeCN, 2 days	T533
[{P4(NEt)6}CuI]n (937)	[P4(NEt)6] (132), CuI/MeCN, 2 days	T81
[{P4(NMe)6}(CuI)2(MeCN)2]n (938)	[P4(NBn)6] (133), CuI/MeCN, 3 days	T81
[{P4(NMe)6}2(CuCl)3(MeCN)2]n (939)	[P4(NMe)6] (131), CuCl/MeCN, 90 min	T526
[{P4(NMe)6}(CuCl)2]n (940)	[P4(NMe)6] (131), CuCl/MeCN, 2 days	T526
[{PN(p-nBuPhP)0.5}4(NMe)6]n (941)	[(PNSiMe3)4(NMe)6] (148), p-nBuPhPCl2/THF, 90 °C, 5 days	T95
[{PN(TiCl2)0.5}4(NMe)6]n (942)	[(PNSiMe3)4(NMe)6] (148), TiCl4/MeCN, 100 °C, 4 days	T95
[Ba(H2O)5][Cr4(OH)4(hpdta)2] (943)	H5hpdta, CrCl3, BaCl2/H2O, 85 °C, 20 h	J119
[Mn4(SPh)8]n (944)	[Mn{N(SiMe3)2}2]2, HSPh/THF, 0 °C, 2 h	C534
[{Cu4{SC(NH2)2}6}2{SC(NH2)2}3]n(SO4)4 (945)	CuSO4, SC(NH2)2, H2SO4/H2O, 80 °C	C187
[N-methylpyridinium]2[{Cu4(dmit)3}2]n (946)	[Cu(MeCN)4][ClO4], Na2dmit, [N-methylpyridinium]I/MeOH	C563
[nBu4N]2[{Cu4(dmit)3}2]n (947)	[Cu(MeCN)4][ClO4], Na2dmit, [nBu4N]Br/MeOH	C563
[(μ3-Cu)Cu4(SePh)6(CuPPh3)3(4,4′-bipy)]n (948)	Cu(MeCOO), PhSeSiMe3, PPh3, 4,4′-bipy/DME, 4 h	C535
{[Et4N][(Ag4(dmit)3]dmf}n (949)	AgNO3, H2dmit, Na, [Et4N]Br, NH3/MeOH, DMF	C564
[(Zn4(SPh)8MeOH]n (950)	HSPh, ZnCO3/MeOH, 55 °C, 5 days	C536
[(Zn4(SPh)8EtOH]n (951)	HSPh, ZnCO3/EtOH, 78 °C, 2 h	C536
[(Zn4(SPh)8nPrOH]n (952)	HSPh, ZnCO3/MeOH, nPrOH, 10 to 97 °C, 5 h	C536
[(Zn4(SPh)8nBuOH]n (953)	HSPh, ZnCO3/MeOH, nBuOH, 10 to 117 °C, 5 h	C536
[(Zn4(SPh)8(trans-1,2-bis(4-pyridyl)ethylene)]n (954)	HSPh, Zn(MeCOO)2, trans-1,2-bis(4-pyridyl)ethylene/H2O, 165 °C, 5 days	B537
[(Zn4(SPh)8(4,4′-bipy)]n (955)	HSPh, Zn(MeCOO)2, 4,4′-bipy/H2O, 165 °C, 5 days	B537
[(Cd4(SPh)8]n (956)	Cd(NO3)2, HSPh, NEt3/EtOH, DMF or [Me4N]2[(CdSPh)3(CdCl)(SPh)6] (447)/MeCN, H2O, 100 °C	C/T232,538
[(Cd4(SC6H4F-4)8]n (957)	Cd(NO3)2, HSC6H4F-4, NEt3/EtOH, DMF	C539
[{Cd6(SC6H4Br-4)15}(CdSC6H4Br-4){Cd(dmf)3}]n (958)	Cd(NO3)2, HSC6H4Br-4, NEt3/EtOH, DMF	C539
[(Cd4(SPh)8PPh3]n (959)	[(Cd4(SPh)8]n (939), PPh3/THF, DMF	I232
[(Cd4(SePh)8]n (960)	CdCl2, HSePh, NaOH/MeOH, H2O	C540
[Cd4(PhSe)7X(PPh3)]n (961–962, X = Cl, Br)	(PhSe)2Cd, CdX2, PPh3/MeOH, 130 °C, 1 h	B541,542
[Hg4(PhSe)7BrPy]n (963)	(PhSe)2Hg, HgBr2, 1,3-bis(4-nitrophenyl)triazene/THF, Py, 100 min	C543
[Hg4(PhSe)7ClPy]n (964)	(PhSe)2Hg, HgCl2, PPh3/THF, Py, 5 h	C544
[Hg4(PhSe)7Br(dmf)]n (965)	(PhSe)2Hg, HgI2, 4,4′-bipy/DMF, 5 h	C544
[Hg4(PhSe)7(SCN)Py]n (966)	(PhSe)2Hg, Hg(SCN)2,/MeOH, THF, Py, 1 h	C545
[Hg4(PhTe)7IPy]n (967)	(PhTe)2Hg, CdI2/THF, Py, 90 min	C546
(C5H5NH2)24[In28Se54(H2O)4] (968)	In, Se, piperidine/H2O, 170 °C, 7 days	B547
(C5H5NH2)24[In28−xBixSe54(H2O)4] (969)	In, Se, Bi(NO3)3, piperidine/H2O, 170 °C, 7 days	B547
[μ3-Se4]3.27[In49.88Se95.92](C5H12N)26.0·(C2H8N)42.4 (970)	Se, In, piperidine/DMF, 170 °C, 5 days	B548
[In4Se10](C7H16N)1.8 (C2H8N)2.2 (971)	Se, In, 1,4-dioxane, 3,5-dimethylpyridine/DMF, 170 °C, 7 days	B548
{[Me4N]2[MnGe4S10]}n (972)	[Me4N]4[Ge4S10] (496), Mn(Me2CO)2/H2O, 24 h or GeS2, Mn(Me2CO)2, [Me4N]Cl, NaHCO3/H2O, 120 °C, 2 days	B/T263,549,550
{[Me4N]2[FeGe4S10]}n (973)	[Me4N]4[Ge4S10] (496), Fe(Me2CO)2/H2O, 24 h or GeS2, FeCO3, [Me4N]Cl, [H4N]HCO3/H2O, 220 °C, 2 days	B/T260,549,557
{[Me4N]2[CoGe4S10]}n (974)	[Me4N]4[Ge4S10] (496), Co(Me2CO)2/H2O, 24 h	T549
{[Me4N]2[ZnGe4S10]}n (975)	[Me4N]4[Ge4S10] (496), Zn(Me2CO)2/H2O, 24 h	T549
{[Me4N]2[Ag2Ge4S10]}n (976)	[Me4N]2[Ge4S10] (496), Na2S2O3, Ag2NO3/H2O, 16 h	T551
{Cs2[FeGe4S10]}n (977)	Cs4[Ge4S10] (493), FeSO4/H2O	T260
{[Me4N]2[Cu2Ge4S10]}n (978)	[Me4N]2[Ge4S10] (496), NaBr, CuCl/H2O, MeCN, 16 h	T551
{[CnH2n+1NC5H5]2[Pt2Ge4S10]}n (979–984, n = 12, 14, 16, 18, 20, 22)	[Me4N]2[Ge4S10] (496), [CnH2n+1NC5H5]Br, K2[PtCl4]/formamide, 80 °C, 18 h	T552
{[(CH3CH2)4N]3[AgGe4S10]}n (985)	[EtNH3]3[MeNH3][Ge4S10] (497), AgOAc, [(Et)4N]Br, methylurea/130 °C, 24 h	T281
{[(Et)4N]3[CuGe4S10]}n (986)	[EtNH3]3[MeNH3][Ge4S10] (497), CuCl, [(Et)4N]Br, methylurea/130 °C, 24 h	T281
{[Me4N]2[MnGe4Se10]}n (987)	[Me4N]4[Ge4Se10] (505), Mn(OAc)2/H2O	T272
{[Me4N]2[FeGe4Se10]}n (988)	[Me4N]4[Ge4Se10] (505), FeSO4/H2O	T272
{[C16H33NC5H5]2[Pt2Ge4Se10]}n (989)	[Me4N]2[Ge4Se10] (505), [C16H33NC5H5]Br, K2[PtCl4]/Formamide, 80 °C, 18 h	T552
{[C16H33NC5H5]2[Pt2Sn4Se10]}n (990)	[Me4N]2[Sn4Se10] (516), [C16H33NC5H5]Br, K2[PtCl4]/Formamide, 80 °C, 18 h	T552
{[Me4N]2[MSn4Se10]}n (991–993, M = Fe, Co, Mn)	[Me4N]2[Sn4Se10] (561), MCl2/H2O	T275
{[Me4N]2[ZnSn4Se10]}n (994)	[Me4N]2[Sn4Se10] (561), ZnCl2, Na4EDTA/H2O	T275
{[Me4N]4[(Ge4S10)Cu4M2S8]}n (995–996, M = Mo, W)	[Me4N]4[Ge4S10] (496), [Me4N]2[MS4], Cu(OAc)2/BuOH, H2O, DMF, 100 °C, 3 days	T553
{[BMIm]2[Ge4Se9]}n (997)	K4[Ge4Se10] (501), SnCl2 2,6-dimethylmorpholine/[BMIm][BF4], 150 °C, 3 days	T554
{[BMMIm]2[Ge4SnSe10]}n (998)	K4[Ge4Se10] (501), SnCl2 2,6-dimethylmorpholine/[BMMIm][BF4], 150 °C, 3 days	T554
{(BMIm)2[SnII(GeIV4Se10)]}n (999)	Cs4[Ge4Se10] (503), SnCl2, 2,6-dimethylmorpholine, [Pt@Bi10][AlBr4]4/(BMIm)Cl, (BMIm)[BF4], 120 °C, 4 days	T555
[Mn2{(OOCC2H4Ge)4S6}(MeOH)(dmf)2]n (1000)	[{HOOC(CH2)2Ge}4S6] (579), MnCl2/MeOH, DMF, 100 °C, 24 h	T556
{[Me4N]2[Mn0.86Co0.14Ge4S10]}n (1001)	GeS2, [Me4N]HCO3, [Me4N]OH, Mn(Me2CO)2, Co(Me2CO)2, H2S/H2O, EtOH, 78 to 150 °C, 3 days	G549
{[Me4N]2[CdGe4S10]}n (1002)	GeS2, CdSO4, [Me4N]Cl, [H4N]HCO3/H2O, 220 °C, 2 days	B557
{(H2dabco)[MnGe4S10]}n (1003)	GeS2, MnCl2, dabco/H2O, CO2, 120 °C, 7 days	B558
{(H2dabco)(H3O)[AgGe4S10]}n (1004)	GeS2, Ag(OAc), dabco/H2O, 130 °C, 2 days	B559
{[Et4N]2[Cu2Ge4Se10]}n (1005)	GeS2, Cu(OAc), [Me4N]HCO3/H2O, 150 °C, 1 day	B560
{[Me4N]6[(Cu0.44Ge0.56S2.23)4(Ge4S8)3]}n (1006)	GeS2, [Me4N]HCO3, Cu(OAc)2, [Me4N]Cl/150 °C, 24 h	A561
{[Me4N]2[MnGe4Te10]}n (1007)	1. K2Te, Te, Ge/heat to melt	E275
	2. [Me4N]Br, MnCl2/en, 100 °C, 12 h
{[Li4(H2O)8][MnGe4Se10]}n (1008)	1. LiSe2, Ge, Se/heat to melt	E282
	2. MnCl2/MeOH, H2O, 24 h
{[Pr2NH2][PrEtNH2][Ge4S9]}n (1009)	GeS2, [Pr2NH2]Cl, NaHCO3/H2O, 125 °C, 24 h	B562
{[Me4N]2[OSn5Se10]}n (1010)	Sn, Se, [Me4N]OH,/H2O, 150 °C, 16 days	B278
δ-GeS2 (1011)	[Me4N]4[Ge4S10] (496), HCl/H2O, 50 °C, 24 h	I266

^admit = 4,5-dimercapto-1,3-dithiole-2-thionato, EDTA = ethylenediamine-tetraacetate, BMMIm = 1-butyl-2,3-dimethyl-imidazolium.

1,3,5,7-Tetraphenyladamantane postfunctionalization (1016).

R =	Reagents/conditions	Ref.
Br (1035)	Br2/CHCl3, −78 °C, 12 h, 60%	616
Br (1035)	Fe, Br2/50 °C, 12 h, 94%	617
Br (1035)	Fe, Br2/70 °C, 7 h, 36%	618
I (1036)	PhI(CH3CO2)2, I2/CHCl3, 12 h, 80%	619
SO2Cl (1037)	HSO3Cl/1.6 h, 57%	620
NO2 (1038)	HNO3, Ac2O, AcOH/30 min, 35%	621 and 622
COCH3 (1039)	AlCl3, CHCOCl/16 h, 68%	626
CHO (1040)	TiCl4, CH3OCHCl2/CH2Cl2, −10 °C to rt, 12 h, 84%	623

1,3,5,7-Tetrakis(4-iodophenyl)adamantane (1036) postfunctionalization^a.

R =	Reagents/conditions	Ref.
OMe (1041)	Cu(i)Br, NaOMe/MeOH, DMF, 100 °C, 12 h, 47–52%	587, 622
CN (1042)	CuCN/DMF, 160 °C, 16 h, 82%	625
PO(OEt)2 (1043)	1. HPO(OEt)2, PdCl2(PPh3)2, Et3N/PhH, 80 °C	627
	2. HCl/reflux, 76%
Pyrrole (1044)	R–H, CuI, K2CO3, N,N-dimethylglycine/DMSO, 120 °C, 21–42%	628
Carbazole (1045)
Imidazole (1046) benzimidazole (1047) phenylimidazole (1048)	R–H, CuI, K2CO3, N,N-dimethylglycine/DMSO, 120 °C, 5 days, 35–43%	628
2-CH3-imidazole (1049)	R–H, CuI, K2CO3, N,N-dimethylglycine/DMSO, 120 °C, 5 days, 41%	629
N(4-OMePh)2 (1050)	R–H, Pd(OAc)2, tBuOK, tBu3P/toluene, 140 °C, 48 h, 72%	630
Ph (1051)	R–B(OH)2, Pd(PPh3)4, NaOEt/EtOH, PhH, 80–100 °C, 24 h, 35–45%	619 and 632
Ethynyl (1052)	1. Me3Si-ethynyl, Et3N, [PdCl2(PPh3)2], CuBr/80 °C, 72 h	621
	2. KF/CH3OH, 50 °C, 12 h, 74%
Ethynyl (1052)	Me3Si-ethynyl, Pd(PPh3)2Cl2, CuI, Et3N, KF/MeOH, 5 days, 81%	621 and 631
I(OAc)2 (1053)	MCPBA/CH2Cl2, AcOH, rt, 12 h, 97%	633
Stilbenyl (1054)	Styrene, Pd(OAc)2, K2CO3, nBu4NBr, DMA/105 °C, 24%	634

^aMCPBA = m-chloroperbenzoic acid.

We will illustrate examples of molecular structures of all cluster types that were obtained in single-crystalline form. For crystallographic details, we refer to the original literature.

2.1.1. Q/H and Q/group 1 adamantane-type clusters

A number of hydride clusters with (transition) metals have been realized, which most often comprise a central metal tetrahedron with direct metal–metal bonds. They are formally constructed by coordinating all edges of this central element by hydrides. They can be seen as one point in a continuum of related compounds featuring fewer hydrogen atoms or additional (bridging) ones, respectively. Although, those will not be further discussed except for some examples.^5–10 Apart from that, there is one species with lithium coordinated by oxygen atoms.

An N-heterocyclic carbene can coordinate to [Mg(HMDS)₂] (HMDS = 1,1,1,3,3,3-hexamethyldisilazide) and in turn be reacted with PhSiH₃, resulting in the adamantane-type cluster [(MgIDipp)₂(MgHMDS)₂H₆] (1, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, Fig. 1), where the magnesium atoms carry either an IDipp or N(SiMe₃)₂ ligand.¹¹ A calcium congener [(CaTACNMe)₄H₆][B(C₆H₃-3,5-Me₂)] (2, TACNMe = 1,4,7-trimethyl-1,4,7-triazacyclononane) is obtained from an in situ-formed complex [(TACNMe)Ca(CH₂Ph)(thf)_x][B(C₆H₃-3,5-Me₂)] after treatment with H₂ gas under elimination of toluene, with all Ca atoms carrying the same tridentate ligand.¹²

Fig. 1. Examples of adamantane-type compounds with hydrogen or group 1 atoms in the E position: [(MgIDipp)₂(MgHMDS)₂H₆] (1, left (a)), [(ZnIDipp)₂(ZnHMDS)₂H₆] (6, middle (b)) and [{Me₂P(BH₃)CHSiMe₂OLi}₄Li₄(Et₂O)_2.75(thf)_1.25] (10, right (c)). Hydrogen atoms in the ligands are omitted for clarity.

The first transition metal cluster anion in this group, [{(CO)₃Re}₄H₆]²⁻ (in 3 and 4) was formed from [Re₂(CO)₁₀], either by reaction with Na[BH₄]¹³ or by prolonged heating under basic conditions in methanol as one of multiple products.¹⁴

The adamantane-type compound [(Cp*Zr)₄H₆] (5, Cp* = pentamethylcyclopentadienyl) was found as the final piece in a row of tetrahedral compounds with fewer hydrides by reduction of [(μ-H)(μ₃-H)(Cp*ZrCl)]₄ with Na amalgam.⁵ This led to a mixed-valence Zr^II/Zr^III situation in the cluster core.

An analog to the aforementioned [(MgIDipp)₂(MgHMDS)₂H₆] cluster was realized with zinc in [(ZnIDipp)₂(ZnHMDS)₂H₆] (6, Fig. 1).¹⁵ The synthesis strategy runs in parallel as well, with Zn(HMDS)₂ as the metal precursor and dimethylamine borane as a hydride source.

A number of iridium hydride clusters (7–9) could be obtained upon dehydrogenation reactions catalyzed by [Ir(Ime)₂(cod)][BF₄] (cod = 1,5-cyclooctadiene) of glycerol.^16,17 This results in the formation of the hydride as well as CO ligands at the metal center in some cases.

A {Li₄O₆} adamantane-like core can be observed in the larger complex [{Me₂P(BH₃)CHSiMe₂OLi}₄Li₄(Et₂O)_2.75(thf)_1.25] (10, Fig. 1). It is formed as the tetramer of the in situ generated linear molecule Me₂P(BH)CH(Li)Si(Me₂)OLi coordinated by additional solvent molecules.¹⁸

2.1.2. Q/group 13 adamantane-type clusters

Adamantane-type clusters with group 13 atoms in the E position are known for groups 14 to 16, with a few unique examples in each group and without a unifying synthetic route. Additionally, there is also an example with a {Ag₄Ga₁₀} adamantane-type scaffold. A brief description of the formation conditions for all of them is given in the following paragraphs.

Different approaches for the formation of the few known carbon/group 13 adamantane-type compounds have been showcased in the literature. The boron congeners [(RC)₄(R′B)₆] (11–13, Fig. 2) can be synthesized at higher temperatures by pyrolysis of BMe₃ or (Cl₂B)₂CH₂,^19–21 or by a solid state reaction of HC(BEt₂)₃ and BEt₃ in the presence of AlEt₃.²² At room temperature, the rearrangement of (BEt)₃(CMe)₂ to [(CMe)₄(BEt)₆] (14) was observed, induced by elemental potassium and I₂.²³

Fig. 2. Examples of adamantane-type compounds with group 13 atoms in the E position: [(CH)₄(BCl)₆] (12, top left (a)), [Li(thf)₄]₂[(^tBuAs)₄(GaCl₂)₆] (18, top center (b)), Li₂[(^tBuN)₄(AlH₂)₆] (20, top right (c)), Na₂[S₄(BH₂)₆] (21, bottom left (d)), DMPyr₂[S₄(InMe₂)₆] (25, bottom center (e)) and [Ga(C₆H₅Me)₂]₂[{AgGa(OTf)₃}₄Ga₆(OTf)₄] (26, bottom right (f)). Hydrogen atoms in the organic ligands and counterions, if present, are omitted for clarity.

A unique synthetic approach, featuring R₂GaH and alkenes HC≡CR′, leads to the formation of carbagallane adamantane-type structures [(R′C)₄(RGa)₆] (15–17).²⁴ It involves the intermediate formation of dialkyl(alkenyl)gallium compounds, which react with additional R₂GaH to form the clusters under elimination of GaR₃.

Three dianionic group 15 congeners exist. An As/Ga compound [Li(thf)₄]₂[(^tBuAs)₄(GaCl₂)₆] (18, ^tBu = tertiary butyl, Fig. 2) is isolated by a simple condensation reaction of InCl₃ and Li₂As^tBu at low temperatures,²⁵ while the compounds Li₂[(RN)₄(AlH₂)₆] (19–20, R = Me, ^tBu, Fig. 2) are formed by condensation of Li[AlH₄] and [RNH₃]Cl.²⁶

The sulfur containing Na₂[S₄(BH₂)₆] (21, Fig. 2) adamantane-type cluster is obtained by a stepwise condensation reaction of THF·BH₃, and Na[BH₄] with H₂S under elimination of H₂.²⁷ In the reaction, an intermediate species (BH₃)S(B₂H₅) is formed, which reacts with additional H₂S to give the final product. The Se congener is formed via a different species with elemental Se and Na[BH₄]. This leads to Na₂[H₃BSe–SeBH₃] which, under the influence of elevated temperature and BH₃, reforms Na₂[Se₄(BH₂)₆] (22). Both the sulfur and selenium homologs undergo a cation exchange to the Cs compounds (23–24) with CsBr. The only other example of a group 16-based adamantane in this category is DMPyr₂[S₄(Me₂In)₆] (25, Fig. 2), which is a decomposition side product of the six membered ring DMPyr₃[Me₂In(SInMe₃)]₃, which could not yet be synthesized in a pure form.²⁸

The single example featuring a transition metal [Ga(C₆H₅Me)₂]₂[{AgGa(OTf)₃}₄Ga₆(OTf)₄] (26, OTf = O₃SCF₃, Fig. 2) comprises bridging triflate ligands between the gallium atoms, with the terminal gallium moieties connecting to three, and the atoms in the E position to four, ligands.²⁹ It is formed by silver triflate reacting with elemental gallium after ultrasonic activation.

2.1.3. Q/group 14 adamantane-type clusters

An extensive family of silaadamantanes obtained from exchanging some or all carbon positions in organic adamantanes with silicon form the largest group in this section. Targeted ligand substitution has been extensively studied in their case. There are also two publications of Si₄E₆ compounds with Ge and Sn in the E position. In combination with P or As, neutral adamantanes of the type [(E¹⁵)₄(E¹⁴R₂)₆] form a small subset. But at first, we will discuss clusters with metal atoms in the Q position, with an example from group 2, 8 and 10.

2.1.3.1. Group 2/group 14 adamantane-type clusters

This unique group 2/14 adamantane-type, [(μ₄-O)Ca₄(2,6-dimethoxyphenyl)₆] (27, Fig. 3), which is formed around a central oxygen atom, uses the tridentate dimethoxyphenyl group as a templating ligand.³⁰ These ligands bridge the Ca sites both by a carbon atom in the E position, as well as by coordination with their oxygen atoms. The origin of the central μ₄-O atom could not be determined and might stem either from H₂O or O₂ impurities during the inert gas protected reaction, or decomposition of the solvent/ligand.

Fig. 3. Examples of adamantane-type compounds with group 2 and transition metals in the Q position and group 14 atoms in the E position: [(μ₄-O)Ca₄(2,6-dimethoxyphenyl)₆] (27, left (a)), [BMIm]₆[S][{Fe(CO)₃}₄Sn₆I₁₀]₂ (33, center (b)) and [(NiPMe₃)₄(CO)₆] (36 right (c)). Hydrogen atoms and counterions, if present, are omitted for clarity.

2.1.3.2. Group 8/14 adamantane-type clusters

In two studies, Fe clusters have been characterized. In the cluster family [(Fe)₄(aryl)₆(thf)_x] (28–31), the carbon atoms of aryls are found in the E position. These clusters are prepared by reacting Fe(acac)₃ (acac = acetylacetonate) with the aryl Grignard reagent (aryl)MgBr.³¹

In the other study, reactions of SnI₄ and Fe(CO)₅ in ionic liquids lead to Fe/Sn compounds. [BMIm]₂[{Fe(CO)₃}₄Sn₆I₁₀] (32, BMIm = 1-butyl-3-methyl-imidazolium) or [BMIm]₆[S][{Fe(CO)₃}₄Sn₆I₁₀]₂ (33, Fig. 3) depending on the counterion in the ionic liquid.³² They each feature different Sn coordination sites. In 32, three Sn atoms carry two iodo ligands, one is connected to only one iodine and the final two carry one terminal iodine and one bridging μ-I connecting them to each other. The second cluster comprises three tin atoms carrying two iodine ligands, while the other three only connect to one terminal iodide each and are connected via a μ₃-I bridge.

2.1.3.3. Group 8/14 adamantane-type clusters

Group 10 clusters with group fourteen elements in the E position are known for combinations with Ni and Pd.

The first family of such compounds with the general compositon [(NiPR₃)₄(CO)₆] (34–37, Fig. 3) comprise CO bridged Ni tetrahedra with terminal phosphine ligands.^33–35 They are generally prepared by reacting a Ni complex with the desired phosphine and CO gas, if the original complex does not contain such ligands already. These results could be transferred to palladium in the case of [(PdPⁿBu₃)₄(CO)₆] (38).³⁶

2.1.3.4. Group 14/14 adamantane-type clusters

A family of tetrasilaadamantanes of the composition [(RSi)₄(CH₂)₆] has been investigated, with the first examples being obtained in high temperature reactions of either SiMe₄ to form [(SiMe)₄(CH₂)₆] or SiCl₄ and Me₃SiCl in the presence of AlCl₃ to yield [(SiCl)₄(CH₂)₆] (39).^37–40 In subsequent work, access to such compounds was made at considerably lower temperatures and in higher yields. [(SiMe)₄(CH₂)₆] (40, Fig. 4) could be obtained from an AlBr₃ induced rearrangement of (Me₂SiCH₂)₃ at 100 °C, which could then in turn be reacted with Cl₂ and I₂ to form 39 or be treated with Li[AlH₄] to form the hydrogen terminated [(SiH)₄(CH₂)₆] (41).^39,41,42Via both of these routes, tetrasilaadamantanes with mixed methyl and halide positions can be isolated as well.^41–43 These clusters described so far are used as the basis for ligand exchange reactions at the Si sites (Method Q, leading to 42–55), often by exchanging the halides found in various positions.^38,44–46 Asides from derivatization on the silicon atom, the CH₂ moiety can also be a target for lithiation to give stepwise addition of longer C/Si chains (56–60).⁴⁷ Lastly, it was also shown that the ligand of a single Si site can be abstracted to obtain a charged cluster cation [(SiMe)₃Si(CH₂)₆][CHB₁₁Cl₁₁] (61) by reacting the carbocation [Ph₃C]⁺ with [(SiMe)₃SiH(CH₂)₆] (49).⁴⁸

Fig. 4. Examples of adamantane-type compounds with group 14 elements in the Q position and group 14 atoms in the E position: [(SiMe)₄(CH₂)₆] (40, left (a)), [(SiSiMe₃)₄(SiMe₂)₆] (62, center (b)) and [(SiSiCl₃)₄(GeMe₂)₆] (84, right (c)). Hydrogen atoms are omitted for clarity.

Realizing the first purely Si based adamantanes took a 9 step synthesis, the last one being a rearrangement of a tricyclic compound Si₁₄Me₂₄ to [(SiMe)₄(SiMe₂)₆] (62, Fig. 4) reminiscent of a synthesis route to organic adamantanes by Schleyer (see section 2.2).⁴⁹ In recent times, the topic has been reinvestigated, resulting in a streamlined gram scale synthesis method, and strategies for a site selective functionalization, which can lead to one or more methyl groups being substituted at the Q position (63–81).⁵⁰

While the pure silaadamantanes were not obtainable from simple building blocks, compounds with mixed Ge/Si sites were isolated by a mixture of Me₂GeCl₂, Si₂Cl₆ and [ⁿBu₄N]Cl, leading to [(SiSiCl₃)₄(GeMe₂)_6−x(SiCl₂)_x] (82–84, x = 0–2, Fig. 4), with the amount of Ge incorporated rising with the use of higher amounts of [ⁿBu₄N]Cl.⁵¹ In follow up investigations, site selective methylation at the Q position of these compounds was realized using the Grignard reagent MeMgBr (85–87).⁵² It was also possible to obtain the corresponding stannasilaadamantanes [(SiSiCl₃)₄(SnMe₂)_6−x(SiCl₂)_x] ((88–89, x = 1–2) by substituting the Ge component for the higher homolog Me₂SnCl₂ in the reaction.

2.1.3.5. Group 15/14 adamantane-type clusters

[P₄(SiR₂)₆] (90–95) adamantane-type clusters with different ligands R are formed by adding Cl₂SiR₂ to a solution of Na, K and P₄.^53–56 A route to mixtures of such compounds with a heterogeneous ligand sphere (90–92, 96–105) is by the thermolysis of .⁵⁷

The germanium compound [P₄(GeMe₂)₆] (106, Fig. 5) is obtained by a Hg catalyzed reaction of Cl₂GeMe₂,^58,59 while the heaviest congeners [P₄(SnR₂)₆] (107–109) were first suggested to be detected as a side product in the condensation reaction of PH₃ and R₂SnCl₂.⁶⁰ The first larger yield synthesis and crystallographic investigation of 107 (Fig. 5) was carried out after an unexpected rearrangement of P(SnMe₃)₃ catalyzed by [(ZnCl)₂Fe(CO)₄(THF)₂] was observed.⁶¹

Fig. 5. Examples of adamantane-type compounds with group 15 elements in the Q position and group 14 atoms in the E position: [P₄(GeMe₂)₆] (106, left (a)), [P₄(SnMe₂)₆] (107, center (b)) and [As₄(SiMe₂)₆] (110, right (c)). Hydrogen atoms are omitted for clarity.

The analogous [As₄(SiMe₂)₆] (110, Fig. 5) is only found as a side product in the thermolysis of Me₂Si(AsSiMe₃)₂.^62,63

2.1.4. Q/group 15 adamantane-type clusters

Compounds with group 15 atoms in the E position are much rarer than those of the neighboring groups. They are spread around the periodic table with examples known in combination with the elements of groups 2, 8 and 11–15, of which the group 15/15 combination is the most common, comprising nearly half of all known species. Adamantane like scaffolds are only found for the lowest homologues, with NR₂, NR, PR₂ or PR making up the bulk of the known groups in the E position. Approaches to obtain those compounds are very diverse, with no unifying method between the different groups.

2.1.4.1. Group 2/15 adamantane-type clusters

Two studies have investigated Be/N adamantane-type clusters. One publication found the anionic azide compounds [(BeX)₄(N₃)₆] (111–112, Fig. 6) by reactions of Me₃SiN₃ with (Ph₄P)₂[Be₂X₆].⁶⁴ The other investigated the formation of amido adamantanes [(BeNH₃)₄(NH₂)₆]²⁺ (in compounds 113–118) in liquid ammonia from elemental Be with varying counterions.⁶⁵

Fig. 6. Examples of adamantane-type compounds with group 15 atoms in E position: (Ph₄P)₂[(Be₄Br)₄(N₃)₆] (112, top left (a)), [Li(thf)₄]₂[(CdPPh₂)₄(PPh₂)₆] (119, top center (b)), [Li(OEt₂)₃][(HAl)₄(NPh)₆{Li(OEt₂)}₃] (124, top right (c)), [(ⁱPrSi)₄(PH)₆] (129, bottom left (d)), [As₄(NMe)₆] (134,bottom center (e)) and Na₁₀[P₄(NH)₆N₄](NH₂)₆(NH₃)_0.5 (150, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

2.1.4.2. Transition metal/15 adamantane-type clusters

There are only a few examples of group 15 containing adamantanes with transition metals. Two of them can be formed by the addition of Ph₂PH to a metal salt in the presence of ⁿBuLi to yield [Li(thf)₄]₂[(CdPPh₂)₄(PPh₂)₆] (119, Fig. 6) or [Li(thf)₄]₂[Cu₄(PPh₂)₆] (120) depending on the element used.^66,67 Two neutral iron clusters with a [Fe₄]⁶⁺ core, comprising iron centers in a formal oxidation state of +1.5 were investigated.^68,69 One could be obtained with a phosphide ligand, [Fe₄(PⁱPr₂)₆] (121), and the other with a ketimide ligand, [Fe₄(N CPh₂)₆] (122). Both are prepared in the same way as the Cd and Cu adamantanes by reacting the lithiated ligand with a metal salt.

2.1.4.3. Group 13/15 adamantane-type clusters

[(NMe₂)₂AlCl]₂ can dimerize under elimination of NMe₃ to form [(AlCl)₄(NMe₂)₄(NMe)₂] (123), with higher yields achieved in the presence of B₂(NMe₂)₄.^70,71 An anionic derivative [(HAl)₄(NPh)₆{Li(OEt₂)}₃]⁻ (in 124, Fig. 6) featuring a Li capped adamantane is prepared by the combination of PhN(H)Li and AlH₃.⁷²

The only known Al/P adamantane compound, [(Ar^Me6Al)₄(PH₂)₄(PH)₂] (125), is isolated after the reaction of PH₃ with [Ar^Me6AlH₂]₂.⁷³ An example for Ga in the Q position [(PhGa)₄(NHⁱBu)₄(NⁱBu)₂] (126) can be synthesized from [PhGa(NMe₂)₂]₂ and H₂NⁱBu.⁷⁴

2.1.4.4. Group 14/15 adamantane-type clusters

Group 14/15 adamantanes have been investigated for E = P. [(PhSi)₄(PPh)₆] (127) and its germanium congener (128) are obtainable by a simple condensation reaction of PhQCl₃ and K₂PPh.⁷⁵ The same principle can be used for the synthesis of [(ⁱPrSi)₄(PH)₆] (129, Fig. 6).⁷⁶ Another synthesis method, utilizing preformed fragments [Li(tmeda)]₂[C₆H₄(PSiMe₃)₂-1,2] with Si^tBuCl₃, leads to the formation of the asymmetrical [(C₆H₄{P(Si^tBuP)1,2})₃(Si^tBu)] (130).⁷⁷

2.1.4.5. Group 15/15 adamantane-type clusters

Compounds of the type [P₄(NR)₆] form the vast majority of clusters within this group combination. They are mostly obtained by condensation reactions of PCl₃ with RNH₂ (131–133),^78–81 a synthesis strategy which also works when substituting PCl₃ for AsCl₃ to form the lesser investigated congeners [As₄(NR)₆] (134–136, Fig. 6).^82,83 Notably, another method of achieving an adamantane-type topology is a reaction starting from a precursor featuring a P₂N₂ four membered ring, ClP(NⁱPr)₂PNⁱPrSiMe₃, which dimerizes when heated to form the so called double decker-type cluster [P₄(NⁱPr)₆], an isomer to the adamantane-type architecture consisting of two four membered rings bridged by two bridging atoms.^84,85 This cluster will in turn rearrange to the adamantane compound (137); an isomerization that also plays a major role in the chemistry of group 14/16 adamantane-type structures and for one Mn/O cluster. The same rearrangement from the double decker was required to form [P₄(N^tBu)₆] (138), albeit that ball milling was needed instead of higher temperatures to prompt the rearrangement.⁸⁶

These compounds can be used as precursors in ligand addition reactions to the pnictogen. The first one investigated was the addition of MeI resulting in [P₃(PMe)(NMe)₆Me]I (139).^78,79,87 Adding S or O atoms in the form of Me₃NO or elemental sulfur leads to [(OP)₄(NR)₆] (140) or [(SP)₄(NR)₆] (141) respectively. The addition of sulfur can be carried out stepwise to achieve the desired degree of sulfurization (142–145).^80,88–93 The addition of transition metal moieties was also realized by reactions with [Ni(CO)₄] to 131 and 134, resulting in adamantanes with terminal Ni(CO)₃ groups (146 and 147).⁹⁴ The ligand sphere on the phosphorous atom can also be expanded stepwise by introducing a SiMe₃ group in [(PNSiMe₃)₄(NMe)₆] (148), which can subsequently be exchanged for PPh₃ (149).⁹⁵ Lastly, purely inorganic and anionic clusters were obtained by the rearrangement of P₃N₅ with addition of alkaline metal NH₂ salts to yield cluster cores [(PN)₄N₆] (150–151, Fig. 6) with different degrees of protonation.^96,97

2.1.5. Q/group 16 adamantane-type clusters

A group 16 element is the most common atom in the E position of inorganic adamantane-type structures. Examples are known for all groups 2–15 (with the notable exception of monomeric group 10 adamantanes) as well as lanthanides. Most often, the chemistry of the oxo-adamantanes is quite different from its higher congeners, stemming from the unique properties of the elements in the second period. Groups 2 and 4–6 nearly exclusively feature compounds with O atoms in the E position, while the reverse case is observed in the groups 11, 12 and 14, which mainly comprise S, Se and Te. There are a few reoccurring structural motifs and synthetic approaches, especially for clusters with the heavier elements S, Se and Te. One family of chalcogenolate compounds [(QER)₄(ER)₆]^q with differing charges q can often be isolated from simple transition metal salts (groups 7–9 and 11–12) and deprotonated chalcogenols, either through in situ deprotonation or by using metal salts. A variant comprising halides X [(QX)₄(ER)₆]^q or other ligands in the X position is sometimes achievable by the choice of the correct precursor salt or counterion, as well as by exchanging a chalcogenolate in this terminal position.

Chalcogenide adamantane-type clusters of the general composition [(QR_0–3)₄E₆]^q are found in a large family of compounds of the groups 13 and 14 as well as a single example with Ru. They are obtainable by condensation reactions using a metal (pseudo)halide and a chalcogenide source such as alkaline metal chalcogenides, H₂E or (SiMe₃)₂E.

An additional family of purely inorganic adamantane-type clusters [Q₄E₁₀] is found for the groups 13–15. They are mostly accessible from the elements and simple salts by Methods A–C or by extracting alloys in accordance with Method E.

2.1.5.1. Group 2/16 adamantane-type clusters

In group 2, a Be hydroxide cluster Na₂[(BeOH)₄(OH)₆] (152) is reported to form from BeSO₄ in basic aqueous solution.⁹⁸ Two further oxygen centered species are obtainable with Ba. One, [(μ₄-O)Ba₄(μ-OC₆H₂(CH₂NMe₂)₃-2,4,6)₆] (153, Fig. 7), is formed with a tridentate ligand, which both delivers the oxygen in the E position and coordinates to the two closest barium atoms via nitrogen atoms.⁹⁹ The other is obtained from a Ba dimer [Ba{N(SiMe₃)₂}₂]₂ assembling around (mes)₂BOH to form [(μ₄-O)Ba₄{OB(mes)₂}₆] (147).¹⁰⁰

Fig. 7. Examples of adamantane-type compounds with group 2–6 elements in Q position and group 16 atoms in the E position: [(μ₄-O)Ba₄(μ-OC₆H₂(CH₂NMe₂)₃-2,4,6)₆] (153, top left (a)), [(μ₄-S)(Tp^Me2Y)₄(SBn)₆] (155, top center (b)), [(TiCp*)₄O₆] (158, top right (c)), [(μ₄-O){Zr(acac)}₄{Zr(OMe)(acac)}(DBcat)₃(OMe)₃] (171, bottom left (d)), [K-18-crown-6]₄[(TaCl₃)₄O₆] (174,bottom center (e)) and (enH₂)[Cr₄(OH)₄(hpdta)₂] (178, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

2.1.5.2. Group 3/16 adamantane-type clusters

[(μ₄-S)(Tp^Me2Y)₄(SBn)₆] (154, Fig. 7) is a unique compound in two ways, as it is both the only group 3 and S centered compound in this review.¹⁰¹ It is created by adding the Y complex [Tp^Me2YBn₂(thf)] with a tridentate ligand to elemental sulfur, which creates the cluster in a redox reaction.

2.1.5.3. Group 4/16 adamantane-type clusters

All but one literature known compound in this category feature a Ti^IV₄O₆ core. The first two examples were cationic in nature, [(TiL₃)₄O₆]⁴⁺, with each Ti exhibiting three bonds to neutral ligands L. For [{Ti(TACN)}₄O₆]Br₄ (156, TACN = 1,4,7-triazacyclononane), this was achieved by hydrolysis of TiO(acac)₂ in the presence of TACN and NaBr,¹⁰² while the second example [{Ti(dmso)₃}₄O₆]Cl₄ (157) was generated in a solution of TiCl₄, Na₂S₄ and PPh₃ in DMSO under partial decomposition of the solvent to yield the required oxygen atoms.¹⁰³

A larger family of neutral compounds contains derivatives of cyclopentadienyl at the Ti centers [(TiCp^R)₄O₆] (158–164, 158 in Fig. 7), mainly obtained through hydrolysis of various Ti cyclopentadienyl complexes or through reactions with other O sources.^104–108

More complex neutral clusters are isolated when the Ti₄O₆ is formally extended by additional M/O fragments. This could be observed for [Ti₄(dmae)₆(OH)(O)₆Cu₆(benzoate)₉] (165, dmae = N,N-dimethylaminoethanolate) and its methyl derivative (166).¹⁰⁹ They form from the respective hydrated Cu benzoates and Ti(dmae)₄ in toluene and feature different coordination modes of the Cu/O fragments.

Two isostructural compounds [{Ti(thf)}₄O₆M₂(TFA)₈(thf)₂] (167–168, M = Fe, Cd; TFA = trifluoroacetic acid) show a symmetric buildup, with the M centers being connected to opposing oxygen atoms in E position and via four TFA groups each to the neighboring Ti centers.^110,111 They are obtained from [Fe₃O(OAc)₆(H₂O)₃]NO₃ (OAc = acetate) or [(OAc)₂Cd(H₂O)₂], and after addition of a Ti complex and TFA in THF.

A highly charged anion [Ti₄O₆(Hcit)₃(cit)]⁹⁻ (in 169, H₄cit = citric acid) is crystallized from a reactive solution of citric acid and [Ti{ⁱPrO)₄] in a H₂O/THF mix. The addition of [Co(NH₃)₆]Cl₃ yields the cobaltate salt, which can be converted to the Na analog (170) by ion exchange chromatography.¹¹²

[(μ₄-O){Zr(acac)}₄{Zr(OMe)(acac)}(DBcat)₃(OMe)₃] (171, acac = acetylacetonate, H₂DBcat = 3,5-di-tert-butylcatechol, Fig. 7), hydrolytically obtained from [Zr₂(acac)₄(DBcat)₂], is a singular Zr example in this group in which half of the E positions are occupied by methoxy groups and half of them by DBcat groups, which also coordinate to one Zr center each.¹¹³

2.1.5.4. Group 5/16 adamantane-type clusters

There are only three unrelated examples of different group 5 oxides in this group.

The vanadium species [(VCp*)₄O₆] (172) stems from a rearrangement of the trimeric species [Cp*V(O)(μ-O)]₃ after addition of PMe₂Ph.¹¹⁴

The cluster compound [{HBO-3,5-(^tBu)₂NbCl}₄O₆] (173, HBO = 2-(2′-Hydroxyphenyl)benzoxazole) is the simple hydrolysis product of [HBO-3,5-(^tBu)₂NbCl₄].¹¹⁵

Using a water containing sample of 18-crown-6 in a reaction of TaCl₅ and K₂S₅ generates the heaviest congener [K-18-crown-6]₄[(TaCl₃)₄O₆] (174, Fig. 7) with an anionic cluster scaffold.¹¹⁶

2.1.5.5. Group 6/16 adamantane-type clusters

Two cationic hydroxo clusters of the type [(CrR)₄(OH)₆]^q+ (in 175–177) can be obtained by hydrolysis of Cr precursor complexes.^117,118 In the case of a combination of CrCl₃ and the pentadentate ligand hpdta (H₅hpdta = hydroxypropanediaminotetraacetic acid), a compound with the cationic cluster [Cr₄(μ-OH)₄(hpdta)₂]²⁺ (in 178, Fig. 7) was isolated, in which two of the oxygen atoms in E position stem from the hpdta ligands.¹¹⁹

The only known Mo congener [{MoO(IPAP)}₄O₆] (179, HIPAP = N-(tert-butyl)-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)-propanamide) is formed as a side product during the reduction of the complex [Mo(O)₂(IPAP)₂] using PPh₃ and could only be isolated in trace amounts.¹²⁰

Two structurally related oxo clusters of tungsten, [(W(O)(tdmap)}₄O₆] (180, tdmap = OC(CH2NMe₂)₃) and [{(W(O)(S-Phoz)}₄O₆] (181, S-Phoz = 2-(4′,4′-dimethyloxazoline-2′-yl)thiophenolate), are known in the literature.^121,122 The first from a reaction of [W(O)(OⁱPr)₄] with Htdmap in the presence of water and the second by rearrangement of the complex [W(CO)(C₂Me₂)(S-Phoz)₂] after oxidation using pyridine-N-oxide.

One sulfide containing adamantane-type cluster [(WPMe₂Ph)₄S₆] (182) exists, which rearranges from the tetranuclear [W₄(μ₃-S)₂(μ-S)₄Cl₂(PMe₂Ph)₆] after reduction with a Na/Hg amalgam in low yields.¹²³

2.1.5.6. Group 7/16 adamantane-type clusters

All known adamantane compounds with an elemental combination of groups 7/16 are Mn clusters in the oxidation state IV, either with oxygen or thiolates in the E position. The oxides are mainly available via hydrolysis and can be derivatized by ligand or ion exchange.

{Mn(TACN)}₄O₆]⁴⁺ (in 183–185) is the first example of such an adamantane-type structure synthesized by addition of simple Mn^II salts to TACN in the presence of water and air to oxidize the metal centers.^125–130

The related adamantane [{Mn(bpea)}₄O₆](ClO₄)₄ (186, bpea = N,N-bis(2-pyridylmethyl)ethylamine) also comprises of an N,N,N-tridentate ligand and cannot be obtained by air oxidation, but requires a comproportionation of two Mn compounds Mn(ClO₄)₂ and [ⁿBu₄N][MnO₄] and bpea.¹³¹ Addition of [ⁿBu₄N]Br yields the bromide salt [{Mn(bpea)}₄O₆]Br 187, which can subsequently be treated with alkaline metal salts for anion exchange (188–192). Methylated bpea can also be used during the synthesis to form derivatives (193–194). The same study also investigated the single electron reduction of the compounds under retention of the adamantane-type scaffold, either by electrochemistry or via TACNMe as a reducing agent (195).

[Mn₄O₆(bpea)₄](ClO₄)₄ can also be used as a basis for ligand exchange using other tridentate ligands (196–200).¹²⁹ In the case of the charged N-substituted iminodicarboxylate ligands, used as their ammonium salts, only partial substitiution products in the form of [{Mn(R-ida)}₂{Mn(bpea)}₂O₆] (201–206, R-ida = N-(R)iminodiacetate) could be isolated as stable compounds.

By a reaction of tame·3HOTf (tame = tert-amyl methyl ether), Mn(OTf)₂ and Et₃N in MeCN and under exposure to athmosperic O₂, the mixed oxo/hydroxo species [{Mn(tame)}₄O₅(OH)](OTf)₅ (207) was obtained, which could be completely deprotonated by additional Et₃N, leading to 208.¹³⁰ Protonation of [{Mn(TACN)}₄O₆]⁴⁺ to the corresponding [{Mn(tame)}₄O₅(OH)]⁵⁺ (in 209) by HClO₄ was also proven to work.

The last literature-known oxide cluster [Mn₄O₄(tphpn)₂](OTf)₂(ClO₄)₃ (210, Htphpn = N,N,N′,N′-tetra-(2-methylpyridyl)-2-hydroxypropanediamine, Fig. 8) features a Mn^III/Mn^IV mixed valency situation and a pentadentate ligand bridging two Mn moieties by coordination with its N sites as well as the O atom in the E position between the two metal centers.¹³² It is prepared by a reductively induced isomerization of the double decker type compound [{Mn₂(μ-O)₂(tphpn)}₂].

Fig. 8. Examples of adamantane-type compounds with group 7–9 elements in the Q-position and group 16 atoms in the E-position: [Mn₄O₄(tphpn)₂](CF₃SO₃)₂(ClO₄)₃ (210, top left (a)), (HPy)₃[{Fe₂(HPhXCG)}₂O(OH)₃] (218, top center (b)), [Et₄N]₂[(FeSPh)₄(SPh)₆] (229, top right (c)), [(RuPPh₃)₄S₆] (235, bottom left (d)), [Co₄(HMPM)₂](ClO₄)₂ (236,bottom center (e)) and [Et₄N]₂[{Co(Cl)}₄(SPh)₆] (241, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

Thiolate complexes with Mn exhibiting adamantane-type structure have also been studied. In the most simple case, dianionic [(MnSPh)₄(SPh)₆]²⁻ clusters (in 211–212) are isolated after conversion of MnCl₂ with NaSPh and an appropriate ammonium countercation.¹³³ Unlike the oxygen species, they contain Mn^II sites in their inorganic core.

In those compounds, all Mn atoms also carry a thiolate ligand which can formally be substituted by halides by either using [Et₄N]Br during the synthesis to form the brominated 213,¹³⁴ or through a rearrangement by adding MnCl₂ to [(Me₄N)₂{Mn₂(SⁱPr)₆}], leading to [Me₄N]₂((MnCl)₄(SⁱPr)₆] (214).¹³⁵ The last method can also yield the corresponding selonlate [Me₄N]₂[(MnBr)₄(SeⁱPr)₆] (215) when using MnBr₂ and [Me₄N]₂[Mn₂(SeⁱPrⁱ)₆] instead.

In [{Mn(BMAP)}₃(MnCl)₃]Cl (216, H₂BMAP = 2-[bis(2-mercaptoethyl)aminomethyl-pyridine), the BMAP ligands coordinate to three of the Mn centers by their N atoms and also carry two thiols each, which make up the atoms in the E position.¹³⁶ The last Mn atom is saturated by a chlorine atom. It forms when adding H₂BMAP to MnCl₂.

2.1.5.7. Group 8/16 adamantane-type clusters

All but one known compounds in this cluster family are iron compounds, which mainly form oxo/hydroxo compounds with polydentate ligands and Fe^III centers, but also Fe^II thiolate complexes common for most transition metal groups.

A family of oxo/hydroxo clusters comprising heptadentate ligands of the type [{Fe₂(L)}₂O_4−n(OH)_n]^q (in 217–221, n = 2, 3, Fig. 8) is obtainable from mostly basic conditions by providing the desired ligand and simple iron salts.^137–141 The ligands in those systems bridge two Fe atoms by providing an O atom in the E position between them and coordinating via three Lewis basic sites to both of them. The charge of the resulting clusters depends on the charge of the ligand and the O/OH ratio. For [Fe₄(N-Et-HPTB)₂O₄][BF₄]₂ (222), obtained from bubbling O₂ through a solution of [Fe₂(N-Et-HPTB)(dmf)₄][BF₄]₃, all of the four E atoms not part of the organic ligand are oxo ligands.¹⁴²

There is a distinctly different arrangement of bridging ligands found in the hydroxo cluster [{Fe(^tBuOH)}₄(dppoe)₄(OH)₆][PF₆]₂Cl₄ (223, dppoe = 1,2-bis(diphenylphosphine oxide)ethane), in which the neutral ligands are not part of the adamantane architechture.¹⁴³ It was unintentionally found to be the main product in a reaction of [(Cp)(dppe)FeCl] (dppe = 1,2-bis(diphenylphosphino)ethane) with the carborane [closo-1,12-C₂B₁₁H₁₀(CN)₂] while in contact to air, oxidizing both the dppe and iron atoms.

Clusters with the non bridging tridentate ligands TACN, [{Fe(TACN)}₄O₂(OH)₄]X₄ (224–225, X = I, CIO₄), do also not comprise oxygen atoms from the ligand in their scaffold and were first obtained after the hydrolysis of [(TACN)₂Fe₂(acac)₂(O)](ClO₄)₂ under addition of NaX,¹⁴⁴ although examples of [{Fe(TACN)}₄O_4−n(OH)_n]^q (in 226–227, n = 2, 3) with different halide counterions could later be synthesized directly from [(TACN)FeCl₃] with a sodium halide in basic solution.^145,146

Thiolate clusters of the form [(FeSR)₄(SR)₆]²⁻ (in 228–230, Fig. 8) and [(FeX)₄(SR)₆]²⁻ (231–232, X = Cl, Br) both exist. The first type is generated by converting FeCl₂ using thiosulfates^147–149 and the second by adding the preformed thiol complex [Ph₄P]₂[Fe(SPh)₄] to FeX₂.¹⁵⁰ [Et₄N]₂[(FeBr)₄(SBn)₆](233) can also be prepared by the first method.¹⁵¹

[{Fe(BMAP)}₃(FeCl)₃]Cl (234) is isostructural to the Mn congener 209 and prepared accordingly.¹³⁶

[(RuPPh₃)₄S₆] (235, Fig. 8) is a singular example, as it is a pure sulfide cluster and the only Ru compound.¹⁵² It can be formed in reactions of a sulfide source like (SiMe₃)₂S or NaSH with PPh₃ and a Ru^II complex like RuCl₂(DMSO)₄ resulting in H₂ or (SiMe₃)₂ as reduced side products.

2.1.5.8. Group 9/16 adamantane-type clusters

There are only a few adamantane-type structures comprising cobalt which are known in the literature.

One, [Co₄(HMPM)₂](ClO₄)₂ (236, H₃HMPM = 2,6-bis[{{(1-hydroxy-2-methylpropan-2-yl)(pyridine-2-ylmethyl)}amino}methyl]-4-methylphenol, Fig. 8), is formed with two heptadentate ligands, which encompass the six oxygen atoms in the E position and coordinate terminally to the Co^II moieties with two N atoms per metal center.¹⁵³ It is formed by combining the deprotonated H₃HMPM ligand and Co(ClO₄)₂.

All other Co adamantane-type clusters are thiolates with a Co^III core. Clusters of the form [{Co(SPh)}₄(SR)₆]²⁻ (in 237–239) are obtained from the thiolates and common cobalt and ammonium salts.^149,154 The terminal thiolates can be formally exchanged by halides, as seen in the compound [^tBu₄N]₂[{Co(Cl)}₄(SPh)₆] (240) formed from [^tBu₄N][CoCl₃(PPh₃)] reacting with PhSSiMe₃ and [Et₄N]₂[{Co(Cl)}₄(SPh)₆] (241, Fig. 8), which in turn forms in a solution of Na, PhSH, CoCl₂ and [Et₄N]Cl.^155,156

A heterogenous substitution pattern is observed for [{Co(Cl)}₂(CoPPh₃)₂(SPh)₆] (242) and [{Co(Cl)}₂(CoPOPh₃)(CoPPh₃)(SPh)₆] (243), which could both be isolated as the products of the addition of PhSSiMe₃ to the complex [CoCl₂(PPh₃)₂], in the presence of O₂ in the second case.¹⁵⁵

2.1.5.9. Group 11/16 adamantane-type clusters

The second largest family of compounds with group 16 elements in the E position is the 11/16 combination. Most of them exist for the elemental combination Cu and S, although some Ag examples and clusters with different chalcogenides are known.

Thiolate containing adamantane-type cluster anions of the general composition [Cu₄(SR)₆]²⁻ (in 244–255) have been extensively studied, and can be obtained by reacting a copper salt with the desired thiolate or by using a monomeric precursor complex already containing the SR species in most cases.^157–169 In some cases, this involves a reduction of the copper atoms from Cu^II to Cu^I.

Different synthetic approaches have also been showcased. An interesting alternative synthesis route features the inversion of Q and E positions during the transformation of the S/Cu adamantane-type structure [(NEt₄]₄[(SPh)₄(CuBr)₆] (847, see section 2.1.7) to the desired [Et₄N]₂[Cu₄(SPh)₆] (256) by addition of [Et₄N]SPh in DMF.¹⁷⁰

The polymer (CuSCH₂CH₂OH)_n decomposes and dissolves in basic aqueous solutions to give the adamantane-type [(ⁿBu)₄N]₂[Cu₄(SCH₂CH₂OH)₆] (257, Fig. 9).¹⁷¹

Fig. 9. Examples of adamantane-type compounds with group 11 in the Q-position and group 16 atoms in the E-position: [(ⁿBu)₄N]₂[Cu₄(SCH₂CH₂OH)₆] (257, top left (a)), [Et₃PPh][μ₃-Cu(CuPEt₃)₃Cu(TePh)₆] (261, top center (b)), [Ph₄P]₂[Cu₄{o-(SCH₂)₂C₆H₄}₃] (262, top right (c)), [Cu₄{SC(NH₂)₂}₆](SO₄)₂ (277, bottom left (d)), [Et₄N]₂[Ag₄(SC₆H₄-p-Cl)₆] (292, bottom center (e)) and [ⁿPr₄N]₂[Ag₄(Se₄)₃] (297, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

An electrochemical synthesis route to the thiolate cluster [Cu(BIK)₂]₂[Cu₄{S(o-tolyl)}₆] (258, BIK = bis(2-methyl-imidazole-2-yl)ketone) is also feasible using a Cu anode in an electrolyte solution of BIK, the thiol HS(o-tolyl) and [ⁿBu₄N]ClO₄ in MeCN.¹⁷²

Analogous reactions can also generate the selenium congener [Me₄N]₂[Cu₄(SePh)₆] (259),¹⁷³ while the only known Te congener [^tBu₃PH]₂[Cu₄(TePh)₆] (260) has been obtained from a rearrangement of the cluster [(^tBu₃P)₃(CuTePh)₄].¹⁷⁴

There is however another tellurium containing adamantane-type structure formally derived from this example. Unlike many other adamantanes discussed here containing a μ₄-atom in the center, this one features a μ₃-Cu atom. One six membered (CuPEt₃)₃Te₃ ring of the adamantane-type scaffold in [Et₃PPh][μ₃-Cu(CuPEt₃)₃Cu(TePh)₆] (261, Fig. 9) coordinates an additional Cu atom in its center opposite to a naked Cu atom in the Q position, leading to a more planar arrangement of the six membered ring.¹⁷⁵ Isolation was possible if Te(Ph)SiMe₃ was used as a tellurolate source in a solution with CuCl and PEt₃.

A related family of adamantane-type ions [Cu₄(SRS)₃]²⁻ (in 262–274, Fig. 9) comprises bridging bis-thiolates in the E position. This leads to two different copper sites: three copper moieties are coordinated by two sulfur atoms of the same bis-thiolate and one from another, while the last Cu atom is coordinated by three different ligands.

Their synthesis normally follows the same patterns as has been discussed for the monothiolates,^176–181 although two examples can be found that form by rearrangement of other copper thiolate compounds.^179,182,183

A purely inorganic S₄ bridge in place of a bis-thiolate could also be observed in the compound [Ph₄P]₂[Cu₄(S₄)₃] (275), prepared from a reaction of elemental sulfur, H₂S and Cu(OAc)₂, thus involving a reduction of the copper atoms.¹⁸⁴

Utilizing neutral thiones in place of thiolates results in the formation of cationic adamantanes of the type [Cu₄(SCR₂)₆]⁴⁺ (in 276–280, Fig. 9).^185–189 This is achieved by addition of the thione to simple copper salts, mostly nitrates or sulfates, in common solvents. Depending on the concentrations and additives used, additional thione ligands can also coordinate to one or multiple Cu sites in the cluster, expanding their coordination number from three to four (281–283).^185,190,191 When choosing CuI as a precursor, such an addition of iodide is observed on all copper atoms, resulting in neutral clusters [(CuI)₄(SR₂)₆] (284–285).^192,193 A Cl homolog [(CuCl)₄{SC(NH₂)NHCH₂CH CH₂}₆] (286) is observed in an electrochemical reaction at copper electrodes in an electrolyte of CuCl₂, HCl and SC(NH₂)NHCH₂CH CH₂ in ethanol.¹⁹⁴

Using linked phosphine sulfides or selenides (EPPh₂)₂N⁻ (E = S, Se) results in cluster cations [Cu₄{(EPPh₂)₂N}₃]⁺ (in 287–290) with the same architecture as described for linked thiolates.^195–198

[Cu₄(O₃N₄)₂](ClO₄)₂ (291, H₃O₃N₄ = 1-Me-4-OH-3,4-bis(CH₂N(CH₂C₅H₄N)(CMe₂CH₂OH)–C₆H₂) represents the only example of a Cu^II as well as a Cu/O cluster compound. The two ligands deliver three oxygen atoms in the E position and additionally coordinate to two copper atoms each via four N moieties, resulting in a heptadentate coordination.¹⁹⁹ Despite the differences, the reaction pathway is similar to the thiolate route as the ligand is deprotonated before reaction with a simple copper salt.

While fewer examples for silver exist, they can generally be seen as the simple heavier congeners of known Cu compounds. [Et₄N]₂[Ag₄(SC₆H₄-p-Cl)₆] (292, Fig. 9) results from transferring the chemistry of simple Cu thiolates to silver,¹⁶⁶ while [Ph₄P]₂[Ag₄{o-(SCH₂)₂C₆H₄}₃] (293) and [ⁿBu₄N]₂[Ag₄(FcSe₂)₃] (294, Fc = ferrocenyl) can be isolated when using a bis-thiolate or bis-selenide respectively.^200,201

Another silver thiolate could be found as the anion in an intercluster compound [Et₄N][Br@Ag₈(2-TBI)₁₂(SO₄)₂][Ag₄(2-TBI)₆(SO₄)₃]₂ (295, 2-TBI = 2-thiobenzimidadzol) together with an octomeric cluster, in which it is additionally coordinated by three sulfate ions. While the reactants are similar to those used in other reactions leading to thiolate adamantanes, solvothermal conditions and ultrasonic activation are used in this case.²⁰²

The only Te homolog in this compound family is found in [Ph₄P]₂[Ag₄(C₄H₃STe)₆] (296). The ligand of this cluster is made by addition of elemental Te to thiophene in the presence of ⁿBuLi.²⁰³

An oligoselenide-containing cluster [ⁿPr₄N]₂[Ag₄(Se₄)₃] (297, Fig. 9) in analogy to the sulfide congener could also be obtained after using Na₂Se₅ as the selenide source.²⁰⁴

The nitrogen bridged phophine selenide [Ag₄{(SePPh₂)₂N}₃](OTf) (298) is another example of a silver compound that can be prepared according to the synthesis used for its copper homolog.²⁰⁵

Lastly, a second selenone [(AgPPh₃)₄(Mbis)₃](OTf)₄ (299, Mbis = 1,1′-methylenebis(3-methylimidazoline-2-selone)) unique to the chemistry with silver results from the addition of Mbis to [Ag(OTf)(PPh₃)], which leads to an adamantane featuring PPh₃ terminal ligands at the silver positions.²⁰⁶

2.1.5.10. Group 12/16 adamantane-type clusters

This family of compounds has been studied systematically in regards to the influence of different ligands, elemental combinations and counter ions. Most of the studies on Zn compounds could be transferred to their cadmium and, unusually for period 6 elements, also to their Hg homologs. While the number of compounds investigated is very high, the types of compounds are not as diverse as for other combinations. With the exception of two clusters, all of them feature chalcogenolate groups in the E position. In the simplest case, this leads to anions of the type [(MER)₄(ER)₆]²⁻ (M = Zn, Cd; E = S, Se, 300–319, Fig. 10).

Fig. 10. Examples of adamantane-type compounds with group 12 in the Q-position and group 16 atoms in the E-position: [Et₃NH]₂[(ZnSPh)₄(SPh)₆] (300, top left (a)), [Me₄N]₂[(CdBr)₄(SPh)₆] (412, top center (b)), [(HgPPh₃)₂(HgBr)₂(Te^oPy)₆] (450, top right (c)), [Cd₂(CdPPh₃)₂(SⁱPr)₆][ClO₄]₂ (464, bottom left (d)), [2.2.2]-cryptH₂[(ZnI)₄(MeO)₆] (465, bottom center (e)) and [Zn₄(POPYH)₃Cl] (466, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

While the first such compounds were obtained from electrolysis of metal anodes in basic thiol solutions,^207,208 a simpler method involving reactions between chalcogenolate solutions and simple non-halide metal salts at mostly room temperature has subsequently been used.^{148,209–222}

In solution, Cd clusters can exchange chalcogenolates, including partial substitution with tellurium, to form mixed compounds [Cd₄(ER)_n(E′R′)_10−n]²⁻ (in 320–368) by reacting them with , or in equilibrium reactions with other similar clusters.²²² The latter strategy also works to form the mixed metal compound [Me₄N][Cd_nZn_4−n(SPh)₁₀] (369–371).

By utilizing a zwitter-ionic thiolate 4-(trimethylammonio)benzenethiolate (Tab), the cationic adamantane in [(MTab)₄(Tab)₆][PF₆]₈ (372–373, M = Zn, Cd) can be isolated by the above described method.²²³

The terminal chalcogenolates can be formally replaced by halides (374–433, Fig. 10). This can be done by ligand exchange reactions with PhICl₂, Br₂ or I₂,^214,224 or during cluster formation by using halide salts, which can also be used to stabilize Hg clusters including rare examples of Hg₄Te₆ scaffolds.^225–230

As described for the pure chalcogenolate clusters, mixed metal adamantanes [Et₄N]₂[(MI)₄(M′I)_4−n(SⁿPr)₆] (434–442, M = Zn, Cd, Hg, Fig. 10) can be obtained by exchange reactions between homometallic congeners.

Asymmetric substitution at the terminal position is possible as well. Depending on the ratio and chalcogenide used, anions of the type [(MX)_n(SR)_4−n(SR)₆]²⁻ (443–447, M = Zn, Cd; X = Cl, Br) can be isolated.^210,231,232 Trying to obtain the HgI/SePh compound with a [(Ph₃P)₂N]⁺ countercation resulted in a charge reduced anion [Hg(HgI)₃(SePh)₆]⁻ (in 448) with one Hg site not carrying any ligand.²²⁵

To reduce the negative charge of the cluster compounds, replacement of the terminal anionic ligands used previously with neutral lewis basic ligands like phosphines or arsines was necessary. With mercury, the neutral compounds [(HgPPh₃)₂(HgX)₂(Te^oPy)₆] (449–451, X = Cl, Br, I; ^oPy = ortho-pyridyl) and [(HgPPh₃)₂(HgSePh)₂(SePh)₆] (452) with mixed terminal ligands were obtainable when using halide or acetate mercury salts.^233,234 A complex precursor [M(L)₂(ClO₄)₂] (M = Cd, Hg; L = PPh₃, PEt₃, AsPh₃) in combination with M(ER)₂ (E = S, Se) and free L leads to cationic clusters in [(ML)₄(ER)₆][ClO₄]₂ (453–464, Fig. 10).^235–237 With certain L and R combinations, this can lead to clusters with a few terminally uncoordinated M sites, which do not, however, influence the charge.²³⁵

There are only two examples with oxygen in the E position. One, the methanolate cluster [2.2.2]-cryptH₂[(ZnI)₄(MeO)₆] (465, [2.2.2]-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, Fig. 10) is obtained in a simple reaction of ZnI₂ and [2.2.2]-crypt in MeOH in which the cryptand acts as a base.²³⁸

The other example, [Zn₄(POPYH)₃Cl] (466, POPYH₄ = N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide, Fig. 10) is formed by the partially deprotonated multidentate ligand coordinating to ZnCl₂, and comprises two different Zn sites.²³⁹ Three are coordinated by two oxygen and two nitrogen atoms of one ligand and one oxygen of another, while the last connects to three different ligands via their oxygen atoms and carries an additional terminal Cl ligand.

2.1.5.11. Group 13/16 adamantane-type clusters

Some group 13 examples with Al, Ga and In are known, although no examples with Te have been observed so far. The simplest examples of group 13/16 adamantane-type structures are [Q₄E₁₀]⁸⁻ (467–469, Fig. 11) anionic clusters, which were the first to be realized for Ga/S, In/S and In/Se from the binary Q₂E₃ and K₂E in water.²⁴⁰ The only other example of such clusters is [H₂dap]₄[Ga₄Se₁₀] (470, dap = 1,2-diaminopropane), also synthesized in aqueous solution, but directly from the elements and dap in solvothermal conditions.²⁴¹

Fig. 11. Examples of adamantane-type compounds with group 13 elements in the Q-position and group 16 atoms in the E-position: K₈[Ga₄S₁₀] (467, left (a)), [enH₂][Al₄(OH)₄(hpdta)₂] (485, center (b)) and [(μ₄-O){(Me₃Si)₃CIn}₄(OH)₆] (486, right (c)). Hydrogen atoms and counterions, if present, are omitted for clarity.

Derivatization of the cluster archetype by protonation of the terminal sulfur atoms was presented for two compounds [(InSH)₄S₆]⁴⁻ (in 471–472) with ammonium counterions, prepared by Method B.^242,243 The addition of a larger fragment was reached in {[Ni(tepa)]₂SO₄}[Ni(tepa)(GaSH)₄S₆] (473, tepa = tetraethylenepentamine), which additionally comprises of a Ni complex coordinated by the cluster, obtained solvothermally from NiS, Ga and tepa.²⁴¹

Formally substituting the terminal chalcogenides by neutral amine ligands yields neutral compounds [(QNR₃)₄S₆]. A condensation of Me₃N·AlH₃ and (SiMe₃)₂S forms the Al congener [(AlNMe₃)₄S₆] (474),²⁴⁴ while a Ga cluster [(GaNH₃)₄S₆] (475) is isolated after the solvethermal reaction of Ga, S and [NMe₄]Cl in hydrazine hydrate.²⁴³ A compound with a slightly larger ligand [(4-Me₂N–C₅H₄NGa)₄S₆] (476) could be achieved in a two step synthesis via an intermediate [(4-Me₂N–C₅H₄N)GaSH_0.64Cl_0.36] formed by (SiMe₃)₂S and the ligand decorated GaHCl₂ species, which can then be converted to the target compound by an additional ligand.²⁴⁵

Another way to achieve neutral clusters is the partial functionalization of the chalcogenides in the E position observed in [(MI)₄(SMe)₄S₂] (477–478, M = Al, Ga), prepared by solid state reactions from binary or elemental compounds.^246,247

Hydroxo clusters of indium [(TACNIn)₄(OH)₆]⁶⁺ (479–480) were the first oxygen species reported, synthesized at room temperature by InCl₃ and TACN in basic aqueous solution in the presence of different counterions.²⁴⁸

By utilizing a formally negative ligand, the charge reduced dication [(BuGa)₄(OH)₆][CHB₁₁Br₆Me₅] (481) with a carborane counterion was obtained from hydrolysis of a low coordinate Ga complex.²⁴⁹

Another cluster type counterion is observed in [{(Me₃Si)₃Si}₄Ga₄O(OH)₅][{(CO)₃Fe}₃{GaSi(SiMe₃)₃}₂{GaFe(CO)₄}] (482), which comprises a central Ga₄O(OH)₅ adamantane-type structure with mixed E sites decorated by hypersilyl groups (Si(SiMe₃)₃) leading to a monocationic cluster.²⁵⁰ It is formed by a rearrangement of [(Me₃Si)₃SiGaCl]₄ in the presence of Na₂Fe(CO)₄·2 dioxane and NaOH.

Mixed oxo and hydroxo clusters [{(Me₃Si)₃CM}₄O₂(OH)₄] (483–484, M = Al, Ga) can also be isolated as neutral compounds from the stepwise hydrolysis of a precursor complex [(Me₃Si)₃CMMe₂], albeit in low yields.²⁵¹

A pentadentate ligand was used to create a dianionic compound, [enH₂][Al₄(OH)₄(hpdta)₂] (485, en = ethane-1,2-diamine, Fig. 11), in which the hpdta ligands each use one oxygen moiety as a μ-bridging site in the E position while coordinating with the two N atoms and the other four oxygen positions to the Al atoms.¹³⁹ The cluster was isolated after a simple condensation reaction between AlCl₃ and the quintuply protonated ligand H₅hpdta in ethane-1,2-diamine.

Lastly, a single oxo centered cluster [(μ₄-O){(Me₃Si)₃CIn}₄(OH)₆] (486, Fig. 11) is synthesized by reacting the In complex Li[Me₃SiInCl₃] with Li[AlH₄] to obtain a cyclic Li/In hydride compound [(Me₃Si)(H)In(μ-H)Li(thf)₂(μ-H)In(μ-H)(H)(SiMe₃)], which will subsequently hydrolyze to the target compound.²⁵²

2.1.5.12. Group 14/16 adamantane-type clusters

The combination of group 14 and 16 elements entails the most compounds investigated until now. Most examples have been synthesized with the sulfides, selenides and, to a lesser degree, tellurides. Looking at the group 14 element, there are many examples for compounds with Si, Ge and Sn, but only a single one for a compound with Pb.

Two large groups of monomeric compounds can be defined: the first are purely inorganic cluster anions with a formal composition of [Q₄E₁₀]⁴⁻ (487–563, Fig. 12) and their derivatives. They are the analogs to previously discussed group 13 compounds like [Ga₄S₁₀]⁸⁻ but feature many more examples and a lower charge. They are mostly formed from the elements and/or simple binary precursors by the Methods A–C and E, resulting in regular adamantane-type anions with mostly (alkaline) metal or ammonium counterions.^253–282 In a unique synthetic approach, it was also shown that those clusters can be made electrochemically using a Sn₂Se₃ cathode in a [Et₄N]Br electrolyte solution in ethane-1,2-diamine to form [Et₄N]₄[Sn₄Se₁₀] (517).²⁸³

Fig. 12. Examples of adamantane-type compounds with purely inorganic cluster anions with group 14 elements in the Q position and group 16 atoms in the E position: Na₄[Si₄S₁₀] (487, left (a)), [18-crown-6-K]₄[Sn₄Se₁₀] (514, center (b)) and [Mn(en)₃]₂[Ge₄O₆Te₄] (564, right (c)). Counterions are omitted for clarity.

The known [Ge₄E₁₀] cluster compounds are often used as reactants in ion exchange reactions (Method L) to introduce a desired functionality or structural template to the compound, such as larger ammonium cations forming lamellar structures (521–538),^284–286 organic molecules (539–546)^287–291 or transition metal complexes with interesting optical properties(547–551).^289,292,293 The family of clusters with metal complex counterions could also be expanded by starting from elements and binary precursors in solvothermal reactions (Method B) to not only obtain more Ge clusters (552–556),^294–297 but also Sn congeners as well as rare earth containing examples(557–562).^298–300 In one case, the addition of antimony to such a reaction mix of GeO₂ and elemental sulfur led to the formation of a compound with two distinct clusters, [(Me)₂NH₂]₆[Ge₂Sb₂S₇][Ge₄S₁₀] (563), one adamantane-type and another ternary molecule with noradamantane like topology.³⁰¹

Unlike the other compounds in this section, the oxo cluster compound [Mn(en)₃]₂[Ge₄O₆Te₄] (564, Fig. 12) deviates from the strict [Q₄E₁₀]⁴⁻ cluster buildup and carries terminal Te groups at the Q position. It is obtained from a solvothermal reaction of Ge, Te, Mn(OAc)₂ and [Me₄N]I in ethane-1,2-diamine.³⁰²

The other group contains predominantly neutral clusters with mostly organic ligands of the type [(RQ)₄E₆]. While at first reactions were carried out using gaseous H₂E (E = S, Se) and a group 14 halide RQX₃,^303–305 most hybrid materials can be obtained through route D, using a solid or liquid chalcogenide source A₂E (A = alkaline metal, SiMe₃; E = S, Se) to prepare 565–612 (Fig. 13).^306–322 As some of them are sensitive to water, the (SiMe₃)₂E precursors are often advantageous for their solubility in organic solvents. The clusters’ structure is heavily influenced by their organic component. In some cases, this leads to an equilibrium between compounds with an adamantane like cluster core architecture and compounds featuring the previously discussed double decker type (see section 2.1.4).^306,307,323 Especially for tin compounds, back coordinating ligands shift the equilibrium away from the adamantane-type architecture, also resulting in defect heterocubane type arrangements, while some Ge congeners can be obtained in the adamantane topology.³²³

Fig. 13. Examples of hybrid adamantane-type cluster compounds with group 14 elements in the Q position and group 16 atoms in the E position: [{HOOC(CH₂)₂Ge}₄S₆] (579, top left (a)), [(N(SiMe₃)DippSi)₄Te₆] (613, top center (b)), [{(PhSn)₃SnS₆}{(WCp)₃S₄}] (622, top right (c)), [(μ₄-O)Pb₄(OSiPh₃)₆] (626, bottom left (d)), [({Cp*(CO)₂Ru}₂Ge)₄O₆] (628, bottom center (e)) and [(Sn(DMEGqu)Br)₄O₄(OH)₂]Br₂ (630, bottom right (f)). Hydrogen atoms are omitted for clarity.

Reactive organic groups on the adamantanes can be used as a site to introduce new functionality. But to prevent the formation of defect heterocubane or double decker type cluster during the addition of Lewis basic ligands to an adamantane core, back-coordination must be prevented by using inflexible ligands.³²¹

Tellurium containing adamantanes of the [(RQ)₄E₆] type have not been obtained yet by Method D. However, in one example, the silicon cluster [Si₄{N(SiMe₃)Dipp}₄] (Dipp = 2,6-diisopropylphenyl) can be reacted with (ⁿBu)₃PTe to afford the desired [(N(SiMe₃)DippSi)₄Te₆] (613, Fig. 13).³²⁴

In a unique oxidative addition of a Sn^II species N(2,6-ⁱPr₂C₆H₃)(SiMe₃)SnCl with elemental sulfur or selenium, [{N(2,6-ⁱPr₂C₆H₃)(SiMe₃)Sn}₄E₆] (614–615, E = S, Se) were isolated.³²⁵

Aside from purely organic ligands, organometallic fragments have also been used to stabilize adamantane-type clusters by the same RSnX₃ and A₂E method described above, either with {Cp(CO)_xM} fragments (616–618)^326–328 or ferrocenyl ligands (619–620).^329,330

It was also possible to exchange one organic ligand in [(PhSn)₄S₆] with a M₃S₄ (M = Mo, W) fragment under retention of the adamantane framework by simple addition of [Cp(CO)₃MCl] and (SiMe₃)₂S, resulting in [{(PhSn)₃SnS₆}{(MCp)₃S₄}] (621–622, Fig. 13).³³¹

One case, leading to an anionic adamantane-type structure with a gold counterion, could be realized by the rearrangement of a defect heterocubane type cluster [{Me(O)CCH₂CMe₂Sn}₃S₄]Cl combined with a ligand extension to [Au(dppe)₂][{Me(H₂NN)CCH₂CMe₂Sn}₄S₆Cl] (623) in the presence of a gold complex.³³²

Compounds with oxygen in the E position are much rarer with only seven examples, one of which is the only known Pb containing adamantane [(μ₄-O)Pb₄(OSiPh₃)₆] (624, Fig. 13), featuring an endohedral μ₄-O atom and silanolate μ-bridging groups.^333,334624 was isolated after a reaction of plumbocene with Ph₃SiOh in Et₂O.

The stoichiometric hydrolysis of RSiCl₃ with bulky R leads to the formation of adamantane type clusters [(RSi)₄O₆] (625–626, R = ^tBu, ⁱPr), as the polymeric species are inhibited due to steric reasons.³³⁵

A reaction more closely related to the synthesis of the higher chalcogenide congeners is utilized for [{(Me₃Si)₃CSn}₄O₆] (627), which is made by combining (Me₃Si)₃CSnCl₃ with Na₂O.³¹⁷

Two further examples obtained from hydrolysis are stabilized by transition metal fragments (628–629),^336,337 with the last one being a cationic species [{Sn(DMEGqu)Br}₄O₄(OH)₂]Br₂ (630, DMEGqu = N-(1,3-dimethylimidazolidin2-ylidene)quinoline-8-amine) formed by SnBr₄, DMEGqu and H₂O and exhibiting a coordination number of 6 at the Sn center, unusual for adamantane-type structures.³³⁸

2.1.5.13. Group 15/16 adamantane-type clusters

The simplest adamantanes with the combination of 15/16 elements are P₄O₁₀, P₄O₆, P₄S_10, P₄Se₁₀ or As₄O₁₀. They are often used as precursors for further derivatives.

Simple derivatization reactions on [P₄O₆] can be carried out by adding terminal chalcogenide groups to the P moieties, oxidizing them from their +III to a +V state. A straightforward method is the thermal oxidation reaction in the presence of trace amount of water to form [P₄O₇] (631).^339–342 Ligand exchange reactions using [P₄S₁₀] or [P₄Se₁₀] can be used with [P₄O₆] to obtain the series [(P₄O₆S_x] (632–635, x = 1–4) and [(P₄O₆Se_x] (636–638, x = 1–3) with the four fold substituted selenium compound not being achieved due to the lower reactivity of the reagent, which would make temperatures above the decomposition point necessary.^343,344 By employing this strategy and starting from 632, a mixed S/Se compound [(P₄O₆SSe] (639) is accessible as well.³⁴³ [(SP)₄O₆] (635) can also be obtained by reacting [P₄O₆] with elemental sulfur.^345–347 Repeating the reactions with [P₄O₇] gives the corresponding mixed terminated adamantane-type structures [P₄O₇S_x] (640–642, x = 1–3) and [P₄O₇Se] (643), with impurities of [P₄O₈] (644) and [P₄O₈S_x] (645–646, x = 1–2) being found in the sulfur containing reaction mixture.^343,348,349

P₄O₆ could also be used as a non-chelating tetradentate ligand to coordinate to Ni(CO)₄ in a solventless reaction at room temperature.^350–352 Depending on the ratio used, the complexes [P₄O₆{Ni(CO)₃}_x] (647–650, x = 1–4) or [(P₄O₆)_xNi(CO)_4−x] (651–652, x = 2–3) could be obtained if one reactant is given in excess. Using a stoichiometric ratio, the formation of coordination polymers has been reported. Reactions with the iron carbonyl [Fe(CO)₅] can similarly be carried out, but proceed much slower and at higher temperatures (653–656).^351,353

[P₄S₁₀] (657, Fig. 14) is most easily obtained from the elements using Method A, though many methods are available.^354–356

Fig. 14. Examples of adamantane-type with group 15 and lanthanide elements in the Q position and group 16 atoms in the E position: [P₄S₁₀] (657, top left), [{(8-HQ)(p-Cl-C₆H₄)Sb}₄O₆] (658, top center (a)), [(μ₄-O){Ce(L_OEt)}₄O₄(OH)₂] (663, top right (b)), [(μ₄-O){Eu(3-NO₂Tp)}₄(μ₂-OMe)₆] (670, bottom left (c)), [(μ₄-O){(SON)Yb}₄(SON)₄(OH)₂] (671, bottom center (d)) and [(μ₄-O)Dy₄(HL)₃(SCN)₄(H₂O)₂] (672, bottom right (e)). Hydrogen atoms are omitted for clarity.

Arylstibonic acids, RSbO₃H₂, can be used as precursors for adamantane-type structures with six coordinated Sb sites (658–661, Fig. 14) in combination with N,O-chelating ligands which trigger the rearrangement at elevated temperatures.³⁵⁷ A similar compound can also be achieved by treating the C,P-coordinated Sb complex (dpan)SbCl₄ (dpan = 6-diphenylphosphinoacenaphth-5-yl) with a basic aqueous solution, yielding [{(dpan)(OH)Sb}₄O₆] (662).³⁵⁸

2.1.5.14. Lanthanide/group 16 adamantane-type clusters

Lanthanide atoms occupying positions within the adamantane-type scaffolds are only known in combination with oxygen in the E position for a number of oxygen centered compounds. In similarity to clusters with hydrogen (see section 2.1.1), related compounds derived from the adamantane-type architecture, in which some atoms in the E positions are formally replaced by two oxygen bridges are also known, but will not be further discussed here.^359–365 In either case, the lanthanides prefer higher coordination numbers, often resulting in multiple or multidentate ligands.

[(μ₄-O){Ce(L_OEt)}₄O₄(OH)₂] (663, Fig. 14) was the first example of such a compound, featuring the tripodal ligand L_OEt = [Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]⁻³⁶⁶ It was realized by the addition of [Et₄N]OH to [L_OEtCe(NO₃)₃], which led to a mix of oxo and hydroxy bridges. It is possible to treat this compound with H₂O₂, which will result in exchanging the oxo bridges with η²-O₂ units in the Q position (664).

The series of clusters [(μ₄-O){M(3-NO₂Tp)}₄(μ₂-OMe)₆] (665–670, M = Pr–Tb; 3-NO₂Tp = 3-nitrotrispyrazolylborate, Fig. 14) also comprises a tripodal ligand on each metal center, but methoxy groups in the E position.³⁶⁷ The reaction path also involved the formation of the monomeric metal complex by addition of MCl₃ to [Bu₄N][3-NO₂Tp] in the presence of methanol.

Another study resulted in a compound in which most oxygen atoms are part of a bridging ligand directly connected to the metal centers.³⁶⁸ [(μ₄-O){(SON)Yb}₄(SON)₄(OH)₂ (671, SON = (benzothiazole-2-yl)phenolate, Fig. 14) contains SON ligands with two different connecting modes: chelating a single Yb site or connecting two such atoms via one of its oxygens and two E positions.

Two clusters, [(μ₄-O)M₄(HL)₃(SCN)₄(H₂O)₂] (672–673, M = Dy, Eu, Fig. 14), were constructed by arranging the metal atoms stemming from M(SCN)₃ around two polydentate ligands 2-hydroxy-N-[2-hydroxy-3-[(2hydroxybenzoyl)amino]propyl]benzamide (H₃L), which comprise all oxygen atoms in the E position.³⁶⁹

2.1.6. Q/group 17 adamantane-type clusters

Group 17 elements only occur in the E position in adamantane-like structures and mainly in (oxygen centered) copper clusters, although there are a few examples outside of this elemental combination, which will be discussed first. While the compounds with the higher congeners Cl, Br and I comprise no further, or only one, ligand at the Q atom, all examples for species with F carry three ligands to expand the coordination sphere on the Q atom to six. Nearly all compounds are produced from elements or simple binary compounds under addition of an appropriate counterion, which is often important for the formation of an adamantane-type scaffold over other structural motifs.

A study showed the formation of simple anionic [Be₄Cl₁₀]²⁻ compounds (in 674–678) with various cations in solid state reactions of BeCl₂ and chlorides.³⁷⁰

There is an oxygen centered example of a magnesium adamantane-type cluster [μ₄-O{Mg(Et₂O)}₄Br₆] (679, Fig. 15) prepared by directly reacting the Grignard reagent PhMgBr with O₂ in ether.^371,372

Fig. 15. Examples of adamantane-type clusters with group 2 and 4–8 atoms in the Q position and group 17 atoms in the E position: [μ₄-O{Mg(Et₂O)}₄Br₆] (679, top left), [{Nb)NMe₂)₃}₄{Nb)NMe₂)₂}F₅O]Cl₂ (680, top center (a)), [{Nb)NMe₂)₃}₄{Nb)NMe₂)₂}F₅O]Cl₂ (690, top right (b)), [μ₄-O{Cr(thf)}₄Cl₄I₂] (692, bottom left (c)), [μ₄-O{Mn(PⁿPr₃)}₄Cl₆] (695, bottom center (d)) and [H8-HQ]₆[(FeF₃)₄F₆] (697, bottom right (e)). Hydrogen atoms and counterions, if present, are omitted for clarity.

Titanium mostly forms adamantane-type clusters of the composition [(TiF₃)₄F₆]²⁻ (680–685, Fig. 15). All of them are formed from TiF₄ in the presence of an appropriate counterion complex, such as crown ether coordinated alkaline metals, ammonium or phosphonium cations.^373–375 These reactions can be carried out in conventional solvents like MeCN or in liquid HF.

In the presence of a macrocyclic arene during the formation of the adamantane, coordination to two Ti moieties under elimination of two fluorines at each position was observed, leading to [(TiCl₃)₂(Ti₂{da6aH₂(H₂)})F₆] (686, da6aH₆ = p-methyl-dimethyldiazacalix[6]areneH₆).³⁷⁶ Another formal, but this time complete, exchange of the terminal fluorine atoms by chlorine was observed for [C₄mim]₂[(TiCl₃)₄F₆] (687, C₄mim = 1-butyl-3-methylimidazolium) obtained after an ionothermal reaction of TiCl₄ under decomposition of the [BF₄] counterion of the ionic liquid.³⁷⁷

The cage compound [{Nb)NMe₂)₃}₄F₆]Cl₂ (688) is obtainable by a synthesis using NbF₅ and Me₃SiNMe₂ in chloroform and toluene.³⁷⁸ While the anion is exchanged by Br in CH₂Br₂ (689), dissolving the cluster in H₂O exchanges one of the F atoms in the E position with an O atom and eliminates a ligand to form [{Nb(NMe₂)₃}₄{Nb(NMe₂)₂}F₅O]Cl (690, Fig. 15).

A Cr compound [μ₄-O{Cr(thf)}₄Cl₆] (691) with a central oxygen and coordinated solvent molecule very similar to the Mg species 679 was obtained from CrCl₂, ⁿBuLi and LiOH·H₂O in THF.³⁷⁹

Two derivatives with both Cl and I sites in the E position [μ₄-O{Cr(solv)}₄Cl₄I₂] (692–693, solv = THF, tetrahydropyran (thp), Fig. 15), could be found in small quantities while trying to synthesize the methylidine complexes [Cr₃Cl₃(μ-Cl)₃(μ₃-CH)(solv)₆].³⁸⁰

A tungsten congener in oxidation state V+ features an anionic fluorine scaffold in [Cp₂WCl₂]₂[(WF₃)₄F₆] (694), resulting from the comproportionation reaction of WF₆ and [Cp₂WCl₂].³⁸¹

The Mn analogs [μ₄-O{Mn(PR₃)}₄Cl₆] (695–696, R₃ = ⁿPr₃, PhMe₂, Fig. 15) were prepared by bubbling O₂ through an anhydrous solution of [MnI₂(PR₃)].^382,383

Another fluorine cluster [H8-HQ]₆[(FeF₃)₄F₆] (8-HQ = 8-hydroxyquinoline, 697, Fig. 15) was isolated after a solvothermal reaction of FeF₂, FeF₃ and 8-HQ in the presence of HF.³⁸⁴

2.1.6.1. Group 11/17 adamantane-type clusters with a central μ₄-O atom

Compounds with copper form by far the biggest group of this combination. The vast majority of compounds with Cl and Br in the E position comprise a central oxygen atom and will be discussed first.

The first compounds discovered were the neutral Cu^II complexes of the type [μ₄-O{Cu(L)}₄Cl₆] (698–758, Fig. 16) with L being a neutral ligand. They were isolated after an addition of simple CuCl_x to L in the presence of ambient air, hydroxide or CuO.^385–436 In some of those cases, the oxygen source could not be determined and is most likely a H₂O or O₂ impurity in the reaction, or stems from decomposition of the solvent. A deviating synthetic strategy uses oligomeric [LCuCl]_x complexes already containing the desired ligand, which rearrange to the desired product.^437–439 The clusters [μ₄-O{Cu(solv)}₄Cl₆] (707 and 737, solv = MeCN, MeOH) can also be used in ligand exchange reactions to generate different compounds with more Lewis-basic ligands (748–749).^394,440 A unique approach was taken in the formation of [μ₄-O{Cu(Amt)}₄Cl₆] (758, Amt = 1,3-diamino-1,2,2-trimethylcyclopentane), which is formed after the ligand in [Cu(α-CgPAmtHMe)(Cl)][BF₄] (CgP = 1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphatricyclo[3.3.1.1]-decane) decomposes after addition of KHMDS.⁴⁴¹

Fig. 16. Examples of adamantane-type clusters with a central μ₄-oxygen atom, Cu in the Q position and group 17 atoms in the E position: [μ₄-O{Cu(Py)}₄Cl₆] (698, left (a)), [Me₄N]₄[μ₄-O(CuCl)₄Cl₆] (766, center (b)) and [μ₄-O{Cu(nicotine)}₄Br₆] (774, right (c)). Hydrogen atoms and counterions, if present, are omitted for clarity.

Heterogenous substitution is possible as well in cases where multiple coordinating molecules are present (759–765).^{401,442–444}

Anionic clusters can be generated when not all chloride atoms are substituted by a ligand during the reaction.^416,436 When no coordinating ligand is present, tetraanions [μ₄-O(CuCl)₄Cl₆]⁴⁻ (in 766–772, Fig. 16) can be isolated readily with different counterions.^445–451

While not as extensively studied, the Br homologs [μ₄-O{Cu(L)}₄Br₆] (773–779, Fig. 16)^{394,432,452–455} were found to be achievable in a similar way by using the appropriate CuBr_x salts.

The mixed cluster [μ₄-O{Cu(L)}₄Cl_6−nBr_n] (780–807) with n = 0–6 are available from using both CuBr₂ and CuCl₂ during the formation reaction, or by ligand exchange from [μ₄-O{Cu(MeOH)}₄Cl_6−nBr_n] (780–786).^456,457

2.1.6.2. Group 11/17 adamantane-type clusters without central μ₄-O atom

Unlinke the many oxygen centered chloride adamantane-type structures, there is only one example for an oxygen free species besides a binary copper complex, namely in [H₂dpipa]₃[Cu₄Cl₆][Cu₂Cl₆] (808, dpipa = N,N′-dimethylpiperazine), obtained from dissolving elemental Cu in HCl together with dpipa and treating it solvothermally in aqueous solution at 120 °C degree for 24 h.⁴⁵⁹

The analogous Br cluster [Cu₄Br₆]²⁻ (in 809–816) is found in combination with different ammonium, phosphonium and a Mg complex counterions, always available through a reaction of CuBr with the corresponding complex bromide.^460–464 One such cluster (806) was also found in a side reaction during the catalytical C–C bond formation between allyl bromide and a (C₆F₅)⁻ ligand from a mixed Cu/Al complex.⁴⁶⁵ The congener of the only known Cl species discussed before [H₂dpipa]₃[Cu₄Br₆][Cu₂Br₆] (815) is synthesized in an analogous way by exchanging HCl with HBr.

Even larger complexes can be found in the compound [Ti₁₂(μ₃-O)₁₄(OⁱPr)₁₈][Cu₄Br₆] (816), in which a polyoxotitanium cluster formed alongside the adamantane when treating CuBr with [Ti(OⁱPr)₄] under solvothermal conditions.^466,467

There is only one example of a compound with a [Cu₄Br₆] inorganic core carrying terminal ligands: [{Cu(Hdabco)}₄Br₆](HCOO)₂ (817, dabco = 1,4-diazabicyclo[2.2.2]octane). It is isolated from CuBr and dabco, and contains [{Cu(Hdabco)}₄Br₆]²⁺ cations forming loose networks by hydrogen bonding between the cluster units.⁴⁶⁸

Synthethic strategies for the preparation of [Cu₄I₆]²⁻ (in 818–832, Fig. 17) are generally the same as for the bromide compounds. Simple species with ammonium, arsonium or phosphonium are isolated after reactions of CuI, or alternatively Cu and I₂, with an appropriate complex salt (818–823).^469–473 Another type of counterion often used are alkaline metal complexes with multidentate ligands such as crown ethers (824–827).^474–476 They are accessible through iodine salts of Cu and the alkaline metal used, if a polyether of the appropriate size is present. [Cu₄I₆]²⁻, similar to its Br congener, is also present as a counterion with other complexes of interest. It is found either as the sole anion or together with [Cu₂I₄] in compounds with phosphine Mn complexes, depending on the phophine used (828–829).⁴⁷⁷ Reaction conditions apart from the nature of the ligand stay the same: MnI₂ and CuI are reacted with R(PPh₂O)₂. Similarly, (BPPIP)[{(BPPIP)Cu₂I₃}₂][Cu₄I₆] (830, BPPIP = Bis-triphenylphosphonio-isophosphindolide) comprises an additional phosphine coordinated linear Cu₄I₆ complex besides the adamantane.⁴⁷⁸ This formation of multiple Cu/I complexes in one compound is also observed for K[K(12-crown-4)]₆[Cu₄I₆][Cu₈I₁₃] (831), prepared according to the strategy described for other ether complex species.⁴⁷⁹ This showcases the importance of the nature of the counterion for the structural motif of the cluster ion.

Fig. 17. Examples of adamantane-type clusters without a central μ₄-oxygen atom, group 11–13 elements in the Q position and group 17 atoms in the E position: [(C₇H₁₆)₄N]₂[Cu₄I₆] (821, left (a)), [{Cp*NbClO}₃][(Cp*Nb)₃Cl₂O₃OH][(ZnCl)₄Cl₆] (833, center (b)) and [H₃dien]₂[Al₄F₁₈] (835, right (c)). Counterions are omitted for clarity.

Lastly, the Cu/I-adamantane motif is observed as a counterion to a three dimensionally extended metal organic framework [Co(tib)₂][Cu₄I₆] (832, tib = 1,3,5-tris(1-imidazolyl)benzene) after a reaction of CoO, CuI and tib according to Method B.⁴⁸⁰

2.1.6.3. Group 11/12 adamantane-type clusters

A very complex compound [{Cp*NbClO}₃][(Cp*Nb)₃Cl₂O₃OH][(ZnCl)₄Cl₆] (833, Fig. 17) featuring two cationic Nb clusters and [(ZnCl)₄Cl₆]²⁻ was observed when reducing the bimetallic trigonal bipyramidal complex [(Cp*NbCl₂)₂ClO(OH)] with Zn in the presence of ZnO.⁴⁸¹ It was also found as the counterion in [(Cp*TaCl)₃O₃(OH)₂][(ZnCl)₄Cl₆] (834), obtained from a similar reaction of Zn, O₂ and [(Cp*TaCl₂)₂Cl₂O].⁴⁸²

2.1.6.4. Group 11/13 adamantane-type clusters

In group 13, [Al₄F₁₈]⁶⁻ (in 835–837, Fig. 17) with varying organic countercations are obtained by solvothermal methods using microwave heating from Al(OH)₃ and HF.^483–485 In these compounds, each Al site carries three terminal fluorine ligands.

2.1.7. Q/transition metal adamantane-type clusters

Some uncommon examples of transition metals in the E position can be found in the literature, two of them of clusters with a group 15 element in the Q positon, but mostly with group 16 elements occupying that site. The metals in the E position belong to the transition metals of group 10–12. The structure of the adamantane can vary in its degree of distortion depending on the elements used, as well as the ligands and the possible presence of a central atom. They were often observed by serendipity or as by products for other target compounds. This is reflected in the synthetic methods not following a trend and differing from cluster to cluster.

The cyclic Q/Zn complexes [ZnI₂{Q(SiMe₃)₃}]₂ (Q = P, As) can be prompted to rearrange at elevated temperature when offered a proper cation to form the anionic adamantane-type structures [(QSiMe₃)₄(ZnI)₆(thf)₂] (838–839, Fig. 18).^486,487

Fig. 18. Examples of adamantane-type cluster with transition metal atoms in the E position: [ⁿBu₄N]₂[(PSiMe₃)₄(ZnI)₆(thf)₂] (838, top left (a)), [(Pd{(η³-C₃H₅)}₄(OH)₆]CF₃SO₃ (840, top center (b)), [(4-SC₅H₄NH)₄(CuBr)₆] (843, top right (c)), [(SC₆H₄Me-p)₄Ag₆{(Ph₂P)₂Me}₄][PF₆]₂ (852, bottom left (d)), [NMe₄]₅[(μ₄-Mo)S₄(CuCI)₃(CuCI₂)₃] (858, bottom center(e)) and [O₄(anpy)₈Zn₆(ZnEt)₄] (859, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

Hydrolysis of a π-allyl Pd complex with an additional chelating and sterically hindered bispidine ligand leads to the formation of a cationic hydroxo cluster [(Pd{(η³-C₃H₅)}₄(OH)₆]²⁺ (in 840, Fig. 18).⁴⁸⁸

Simple addition reactions can be used to react a preformed Cu complex of a S₂N₂-tetradentate ligand with CuCl to form [Cu(bme*daco)}₂(CuCl)₄] (841, bme*daco = bis(N,N′-2-mercapto-2-methylpropyl)1,5-diazocyclooctane).⁴⁸⁹

In a redox reaction of Cu^IICl₂ with KI and para-4-mercaptopyridine, a poylmeric Cu^I₃I₄ formed as the main product next to an adamantane-type cluster [(4-SC₅H₄NH)₄(CuCl)₆] (842) of neutral pyridine-4-thione and Cu^ICl.⁴⁹⁰ The corresponding bromide compound (843; Fig. 18) could be obtained after cleaving the S–S bond in 4,4′-bipyridyldisulfide at higher temperatures and reacting with CuBr.⁴⁹¹

Two isomers of [Cu₆(phen)₄(SPh)₄Cl₂] (844–845) with differing positions of the chlorine atoms in the cluster scaffold were found after a simple condensation of PhSH with CuO^tBu under the addition of phenanthroline.⁴⁹² The chlorine found in the compound is suspected to stem from decomposition of the solvent CH₂Cl₂.

[NEt₃]X (X = Cl, Br) was found to break up polymeric [CuSPh]_n to initiate a rearrangement to [(NEt₄]₄[(SPh)₄(CuX)₆] (846–847).¹⁷⁰ This cluster could be prompted to reversibly invert its Q and E positions and form [Et₄N]₂[Cu₄(SPh)₆] (256) with an excess of [HNEt₃][SPh], as described before.

Extreme levels of structural distortion are seen in compounds with cationic cluster molecules of the type [(ER)₄M₆{(Ph₂P)₂R}₄]²⁺ (848–857, E = S, Se, M = Cu, Ag, Fig. 18), which are made by combination of dimeric complexes [M₂{(Ph₂P)₂R}₂(MeCN)₂]²⁺ with phosphine ligand bridged metal centers rearranging around RE⁻ units,^493–495 or the reaction of polymeric [AgER]_n with the phosphine ligand.⁴⁹⁶

In one case, an adamantane-type structure could be built around a central [MoS₄] fragment by coordination of the tetrahedral [NMe₄]₂[MoS₄] with CuCl to isolate crystals of [NMe₄]₅[(μ₄-Mo)S₄(CuCI)₃(CuCI₂)₃] (858, Fig. 18).⁴⁹⁷

A [Zn₁₀O₄] oxo adamantane is found at the centre of [O₄(anpy)₈Zn₆(ZnEt)₄] (859, anpy = anilido-pyridinate, Fig. 18). It comprises four terminal ZnEt and six bridging Zn units, which are interconnected by eight bidentate organic ligands. It is obtained from the hydrolysis of ZnEt₂ in the presence of the templating anilido-pyridinate.⁴⁹⁸

2.1.8. Adamantane-type clusters with mixed elements in Q and E positions

Adamantane-type structures comprising elements from different groups in E and Q positions are rare but have been realized in a variety of examples. Most often, a stepwise buildup approach is used, in which different elements are first linked in small molecules, which can then reassemble into the desired adamantane framework.

The earliest example of such a reported compound was the cage compound [S₄(CH₂)₂(BH₂)₄] (860, Fig. 19), which is obtained by using THF-BH₃ gas with the binary synthon and solvent CS₂.⁴⁹⁹ Exchanging the borane for NaB₃H₈ leads to a slightly different reactivity, with only one intact CS₂ unit in the product [S₄(CH₂)(BH₂)₅] (861).⁵⁰⁰

Fig. 19. Examples of adamantane-type clusters with elements from different groups in equivalent positions.: [S₄(CH₂)₂(BH₂)₄] (860, top left (a)), [(ZnCl)₂(ZnPⁿPr₃)₂(PPh₂)₄Cl₂] (862, top center (b)), [{(thf)Mg}₄{Si(SiMe₂^tBu)₂}₂Cl₄] (868, top right (c)), [μ₄-O{(thf)₂Ca}₃MgPh₃Br₃] (869, middle left (d)), [{(1-C{NDippCH₂CH₂N})₂(CH₂)₂PhO}Mg₂(Mg(thf)}₂Br₄] (871, middle center (e)), [PhSi{CH₂Sn(S)Ph}₃] (889, middle right (f)), [As₄(CH₂)₃O₃] (892, bottom left (g)), [μ₄-O(AlMe){(thf)Cl₂Zr}₃(OMe)₆] (894, bottom center (h)) and [H₃TAEA]₂[InGe₄S₁₁(SH)₂(OH)] (911, bottom right (i)). Hydrogen atoms and counterions, if present, are omitted for clarity.

A mixture of Cl and P in the E position results from a stochiometric condensation reaction between four MCl₂ (M = Zn, Cd) and four Ph₂PSiMe₃ molecules under elimination of ClSiMe₃ in the presence of PⁿPr₃ (ⁿPr = normal propy). The resulting [(MCl)₂(MPⁿPr₃)₂(PPh₂)₄Cl₂] (862–863, Fig. 19) features two formally retained MCl₂ fragments bridged by PPh₂ units.⁵⁰¹ The Zn compound was also synthesised with varying terminal phosphine ligands (864–866).⁵⁰²

A preformed complex dimer [(SiMe₃)₃PZnI)I]₂ was observed to form the adamantane-type [ⁿBu₄N]₂[(CdI)₄{P(SiMe₃)₃}₂I₄] (867) after addition of [ⁿBu₄N]I, which also comprises mixed P and halide E sites, albeit with inverse ratios.⁴⁸⁶ This is formally achieved by a dimerization under elimination of two equivalents of (Me₃Si)₃PI.

A similar dimer with a four membered ring-structure [(thf)₂Mg{Si(SiMe₂^tBu)₂}]₂ was rearranged under formal chlorination by ^tBuMgCl·2MgCl₂ to form the adamantane-type dimer [{Mg(thf)}₄{Si(SiMe₂^tBu)₂}₂Cl₄] (868, Fig. 19).⁵⁰³

In the preparation of a calcium cuprate, using a CuPh precursor with residual MgBr₂ from the Grignard reaction carried out in its synthesis can lead to a formal adduct of MgBr₂ to the Ca complex, leading to [μ₄-O{(thf)₂Ca}₃MgPh₃Br₃] (869, Fig. 19) with the central oxygen atom stemming from decomposition of THF.⁵⁰⁴ In this compound, three phenyl groups and three bromides occupy the E positions.

MgBr₂ can also be used in a reaction with a tridentate carbene-ligand-stabilized adduct of lithium hexamethyldisilazide [{1-C(NDippCH₂CH₂N)}₂(CH₂)₂PhOLi₂N(SiMe₃)₂], leading to the substitution of the lithium azide with two MgBr fragments.⁵⁰⁵ As additional products, a symmetric and asymmetric adamantane-type cluster with endohedral μ₄-O atoms were found. The symmetrical compound, [{(1-C{NDippCH₂CH₂N})₂(CH₂)₂PhO}₂Mg₄Br₄] (870), can be understood as a dimer of the carbene stabilized Mg complex, while the asymetrical example, [{(1-C{NDippCH₂CH₂N})₂(CH₂)₂PhO}Mg₂(Mg(thf)}₂Br₄] (871, Fig. 19), has lost one ligand and saturates the Mg moieties with THF.

In group 14/16 adamantane clusters, the group 16 elements in E position can be replaced by isoelectronic CR₂ fragments. Corresponding compounds can be accessed from carbon-bridged fragments, which are connected by intermolecular or intramolecular condensation reactions with the desired group 16 precursor. For tin compounds, this was first shown for a series (872–876, R = Ph, CH₂SiMe₃, R′ = H, E = S; R = Ph, R′ = H, E = Se, Te; R = R′ = Me, E = Se), originating from an precursor reacted with Na₂E or (^tBu₂SnE)₂.⁵⁰⁶ Those compounds were also found to undergo exchange reactions, forming either a cluster with mixed organic ligands, [(PhSn)₂(Me₃SiCH₂Sn)₂S₄(CH₂)₂] (877), by mixing 872 and 873 or clusters with mixed E sites, [(PhSn)₄S_4−xSe_x(CH₂)₂] (878–881) or [(PhSn)₄Se_4−xTe_x(CH₂)₂] (882–885), by mixing 872 with 874 or 874 with 875, respectively. Note that there are two possible isomers for the x = 2 case.

An analogous oxo-cluster, [{(Me₃Si)₂CH₂Sn}₄O₄(CMe₂)₂] (886), was isolated after exposure of {(Me₃Si)₂CH₂SnCl₂}₂CMe₂ to a NaOH solution.⁵⁰⁷

When using a tetrameric precursor RSi(CH₂SnPhX₂)₃ (X = Cl, I) in reactions with a chalcogenide source, the mixed-element clusters [MeSi{CH₂Sn(E)Ph}₃] (887–888, E = S, Se) and [PhSi{CH₂Sn(E)Ph}₃] (889–891, E = S, Se, Te; Fig. 19) were realized, with three instead of two E positions being occupied by CH₂ and also mixed Si and Sn positions.^508,509

Another reaction to mixed adamantane-type structures from preformed precursors is the synthesis of arsenicin A [As₄(CH₂)₃O₃] (892, Fig. 19) from the linear CH₂(AsPhCH₂AsPh₃)₂, which is isolated as a racemic mixture after treatment with HI to halogenate all the As positions and a subsequent hydrolysis with aqueous ammonia.⁵¹⁰

A hydride cluster [(Cp*Ru)₃H₅] can coordinate the primary silane ^tBuSiH₃ in a μ₃-η²:η²:η² mode under H₂ elimination to form the compound [(Cp*Ru)₃(^tBuSi)H₆] (893) with an adamantane-type scaffold.⁵¹¹ Hydrogen atoms can be abstracted to transform the multi center bonds into a simpler Ru–Si contact.

Another method to obtain such mixed adamantane-type structures is the substitution of one atom in an already synthesized cluster. One Zr atom in the previously described cluster [μ₄-O{(thf)Cl₂Zr}₄(OMe)₆] was treated with AlMe₃ to incorporate a AlMe site in the Q position of the compound [μ₄-O(AlMe){(thf)Cl₂Zr}₄(OMe)₆] (894, Fig. 19).⁵¹²

Multiple chalcogenolate clusters comprising transition metals of different groups, and in one study Ga, could be isolated. The earliest study achieves this for [Me₄N][(MSPh)_n(M′SPh)_4−n(SPh)₆] (895–899, M/M′ = Fe/Co, Fe/Zn, Fe/Cd, Co/Zn, Co/Cd) by exchange between the homometallic clusters, as has been described before in this review.¹⁴⁸ Similar compounds [Me₃NBn]₂[(FeCl)₃Cu(EⁱPr)₆] (900–901, E = S, Se) and [ⁿPr₃N(CH₂)₆NⁿPr₃][(FeBr)₃Cu(SePh)₆] (902) with Fe and Cu in the Q positions could also be obtained from a dimeric homometallic precursor complex [Me₃NBn]₂[(Fe₂(EⁱPr)₆] by addition of FeCl₂ and CuCl or from a mixture of CuBr, Fe(OAc)₂ and PhSeSiMe₃, and under addition of [ⁿPr₃N(CH₂)₆NⁿPr₃] counterions in the second case.^513–515

As discussed for the Cu/Te cluster 254 before, there are examples for μ₃-group 11 atoms located at the center of a M₃Te₃ six membered ring. In the following compounds, the Q position opposing this μ₃ metal is occupied by an element from a different group. The first examples of this architecture are [(μ₃-M)(CdPPh₃)(MPPh₃)₃(TePh)₃(μ₃-TePh)₃] (903–904, M = Cu, Ag), prepared from NaTePh, MCl and CdCl₂ in the presence of PPh₃.⁵¹⁶ The Zn congener [(μ₃-Cu)(ZnPⁱPr₃)(CuPⁱPr₃)₃(TePh)₃(μ₃-TePh)₃] (905) was later isolated by a more complex synthetic route starting from a tetranuclear cluster precursor [(PⁱPr₃)₃(CuTePh)₄] which was reacted in a stepwise manner with ZnEt₂, PⁱPr₃ and PhTeSiMe₃.⁵¹⁷ The same motif could also be stabilized for compounds with the main group metal Ga, [μ₃-Cu{Cu(PR₃)₃}₃(GaMe)(EPh)₆] (906–909, E = Se, R = Me, Et, Et₂ⁱPr; E = Te, R = Et).¹⁷⁴ They are obtained after reacting the complexes [(PR₃)₅(CuEPh)₆] with chalcogenidolates and a GaMe source.

A mixed W/Ti oxygen adamantane-type structure [(W(O)OⁱPr)₂{Ti(OⁱPr)₂}₂(O)₄(bdmap)₂] (910, Hbdmap = 1,3-bis-(dimethylamino)-propan-2-ol) was obtained after a reaction of the complex [W(O)(OⁱPr)₃(bdmap)] with Hbdmap and Ti(OⁱPr)₄, followed by a hydrolysis in a H₂O/ⁱPrOH mixture.¹²²

There are also examples of mixed adamantanes accessible directly from the elements and simple binary compounds if the correct additives and conditions are used. [H₃TAEA]₂[InGe₄S₁₁(SH)₂(OH)] (911, TAEA = tris(2-aminoethyl)amine, Fig. 19) is obtained solvothermally from In(NO₃) and GeO₂.⁵¹⁸ Its structure can be understood as a [Ge₄S₁₀]⁴⁻ adamantane-type in which one GeS unit is substituted by an InS₂GeOH(SH)₂ fragment.

An example of two different transition metals in the E position is obtained when using a Ni complex instead of a copper complex in the reaction to give [Cu(bme*daco)}₂(CuCl)₄] (912), leading to the mixed derivative [Ni(bme*daco)}₂(CuCl)₄].⁴⁸⁹

2.1.30. Compounds with extended adamantane-type structure

By formal addition of metal atoms on the outside of an adamantane-type cage, as opposed to endohedral addition as in case of some previously discussed compounds, larger clusters could be obtained while still maintaining an adamantane core structure. As the addition of many atoms leads to totally new structural motifs, only some examples with the addition of only a few atoms and a clear adamantane core will be discussed.

A formal addition of a Cu(PR₃)₂ unit to a [μ₃-Cu(CuPR₃)₃Cu(EPh)₆] (E = Se, Te) core, a structural motif observed in the previously discussed compound 261,¹⁷⁵ leads to the neutral clusters [μ₃-Cu(CuPR₃)₃{Cu(PR₃)₂}Cu(EPh)₆] (913–915).^519,520 The synthesis does not deviate much from the one for the anionic cluster. As in all cases, a Cu salt is reacted with PR₃ and PhESiMe₃, with the resulting compound depending only on the exact chalcogenide or PR₃ used.

A related compound featuring silver atoms [Ag₄{Ag(PEt₃)₂}₂(TeⁿBu)₆] (916, Fig. 20) could be isolated using an analogous route.⁵²¹ Here, both additional Ag(PEt₃)₂ units coordinate on the outside of the cluster, bridging two Te atoms each.

Fig. 20. Examples of compounds with an extended adamantane-type structure: [Ag₄{Ag(PEt₃)₂}₂(TeⁿBu)₆] (916, top left (a)), [Cu₄(CuPⁱPr₃)₃(SePh)₇] (917, top center (b)), [μ₃-(RuPPh₃)(RuPPh₃)₄S₆] (918, top right (c)), [H₃tren]₄[(Al₄F₁₇)₂F]OH (928, bottom left (d)), [Ni{Ni(chp)₂MeOH}₆]Cl₂ (932, bottom center (e)) and [Et₄N]₃[Cu₄Sb(Te₇)(Te₂)₂Te] (935, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

[Cu₄(CuPⁱPr₃)₃(SePh)₇] (917, Fig. 20) is an example of a larger expansion of a [Cu₄(SePh)₆] central adamantane. In this case, by addition of a μ-CuPⁱPr₃ connecting two selenium atoms of the central scaffold and an additional μ₃-(CuPⁱPr₃)₂SePh bridge between three other selenolates, an increase of the coordination number of all but one selenium atoms to 4 is achieved.⁵²⁰

Another structural motif of expanded adamantanes is achieved by formally capping one face of the octahedron formed by the six E atoms with an additional metal fragment. In contrast to some other molecules, we have discussed featuring μ₃ Cu or Ag atoms in the center of a six membered ring of the adamantane-type scaffold, these metal moieties carry additional ligands and are located below the plane of the Q₃E₃-ring, which causes a greater deviation from planarity as opposed to a more planar arrangement when compared to an uncoordinated adamantane-type structure. This effect can be observed in [μ₃-(RuPPh₃)(RuPPh₃)₄S₆] (918, Fig. 20) when compared to the non-coordinated 235 discussed beforehand.¹⁵² The extended compound is obtained by reacting S(SiMe₃)₂ with [Ru(PPh₃)₃Cl₂] in hot THF, as opposed to using NaSH as a sulfur precursor, which leads to less oxidized metal centers.

This architecture has also been explored for two clusters [μ₃-(FeCl)(VPEt₃)(FePEt₃)₃S₆] (919–920, M = V, Mo) capped by a FeCl unit.^522,523 They are also obtained by using S(SiMe₃)₂ and a mixture of the metal complexes [M(thf)₃Cl₃] and [Fe(PEt₃)₂Cl₂]. Sodium thiolates can be used to replace the chlorine atom at the added site by a SR group (921–925).

When NaS₂ is used instead, the cluster will dimerize to [μ₃-{(VPEt₃)(FePEt₃)₃FeS₆}₂S] (926), comprising two adamantane-type cages connected by a μ-S bridge.⁵²⁴ A more distorted example of this dimer buildup is [μ₃-(HgSPh)(AgPPh₃)₃Hg(SPh)₆}₂S] (927), in which the metal atoms on both sites of an Ag₃S₃ ring are Hg atoms.⁵²⁵ This is achieved by forming NaSPh in situ and reacting it with HgO and [Ag(PPh₃)₂]NO₃.

This μ-bridged adamantane topology is also present in two further examples. One is [H₃tren]₄[(Al₄F₁₇)₂F]OH (928, tren = tris(2-ethylamino)amine, Fig. 20), in which two [Al₄F₁₈] clusters are condensed by a μ-F.⁴⁸⁴ It is observed when adjusting the compound ratios in the synthesis of monomeric 836 (see section 2.1.6). The other is [{P₄(NMe)₆}₂CuCl]₂ (929) which was isolated as a side product when reacting an excess of [P₄(NMe)₆] with CuCl besides further polymeric products, that will be discussed in the next section.⁵²⁶

A different type of dimer could first be observed in the compounds [H₂Ta(tdci)₂]CI₃ (tdci = 1,3,5-trideoxy-1,2,5-tris(dimethylamino)-cis-inositol, Hchp = 6-chloro-2-hydroxypyridine, 930) and [H₁₁Ta₇O₁₂(tdci)₆] (931), in which two adamantane-type clusters are condensed by one atom in the Q position.⁵²⁷ The first is an organometallic compound, in which a central Ta is trigonal prismatically coordinated by six oxygen atoms and the adamantane-type scaffolds are completed by hydrocarbons. This is achieved by coordinating tdci to TaCl₅ in methanol. The second compound is obtained after hydrolysis of the first, and features two condensed Ta₄O₆ subunits decorated by tdci ligands on the three non-condensed Ta sites, which in turn resemble an organometallic adamantane-type structure. Thus, this compound could also be described as comprising 8 condensed adamantane-type scaffolds.

A further compound with the same dimer architechture is [Ni{Ni(chp)₂MeOH}₆]Cl₂ (932, Hchp = 6-chloro-2-hydroxypyridine, Fig. 20), made at 130 °C under inert conditions by addition of Ni(OH)₂ and Hchp.⁵²⁸ This compound is notable due to the fact that there are no monomeric group 10/16 adamantane-type structures at all.

Apart from examples with oxygen, there is an Al/F dimer [(C₂H₄NH₃)₃NH]₂·(H₃O)·[Al₇F₃₀] (933), formally made up of [Al₄F₁₈] clusters condensed by an Al site.⁵²⁹ It is obtained by solvothermal conversion from Al₂O₃ with HF.

By formally condensing two adamantanes at a face between a Q and two connected E atoms instead of just by one Q atom, a new structural motif is achievable. This was realized for [{(SiMe)₃(CH2)₄}₂Si(CH)₂] (934), which is formed by two [(SiMe)₄(CH₂)₆] molecules condensed via one face.^530,531 The presence of this compound was confirmed after heating SiMe₄ at 700 °C.

A clear adamantane-type cluster Cu₄Te₆ core is also present in the cluster [Et₄N]₃[Cu₄Sb(Te₇)(Te₂)₂Te] (935, Fig. 20). However, the Te sites are mostly part of oligotellurides.⁵³² One Cu atom coordinates to three sites of a linear Te₇, all of which also coordinate to the three other Cu atoms which form the typical six membered ring opposed to the first copper together with a single Te and two Te₂ units. Lastly these three Te fragments coordinate a Sb atom below the six membered ring. It was obtained by the extraction of the alloy KCuSbTe₃, prepared from K₂Te, Cu, Sb₂Te₃ and Te with ethane-1,2-diamine.

2.1.31. Adamantane-type scaffolds in polymeric structures

Apart from molecular species, networks consisting of linked adamantanes of the type [Q₄E₁₀] can be formed, either by linking previously existing isolated clusters, or by the synthesis of simpler precursors. To limit the scope, we will only discuss corner condensed species as well as those connected by additional linker molecules. This can lead to zeolite like compounds. Such species have been found for the groups E = 15, 16 and 17.

Linking of the previously discussed P/N adamantane-type structures [P₄(NR)₆] (936–938, R = Me, Et, Bn, Fig. 21) can be achieved by the addition CuI to form one dimensional chains of [{P₄(NR)₆}CuI]_n (R = Me, Et) with μ-bridging CuI moieties or [{P₄(NMe)₆}(CuI)₂(MeCN)₂]_n comprising linking CuI and MeCN four membered rings.^81,533 Similarly, reactions of [P₄(NMe)₆] with CuCl lead to a three dimensional network [{P₄(NMe)₆}₂(CuCl)₃(MeCN)₂] (939) or a ladder like one dimensional polymer [{P₄(NMe)₆}(CuCl)₂]_n (940) depending on the cluster to CuCl ratio.⁵²⁶ Ligands on [(PNSiMe₃)₄(NMe)₆] can be exchanged for TiCl₃ or p-ⁿBuPhPCl₂, which polymerize to form extended networks that could not yet be structurally characterized (941–942).⁹⁵

Fig. 21. Examples of networks of type 2 supertetrahedra: [{P₄(NMe)₆}CuI]_n (936, top left), [Mn₄(SPh)₈]_n (944, top right (a)), [(μ₃-Cu)Cu₄(SePh)₆(CuPPh₃)₃(4,4′-bipy)]_n (948, middle left (b)), [Hg₄(PhSe)₇ClPy]_n (964, middle right (c)), (C₅H₅NH₂)₂₄[In₂₈Se₅₄(H₂O)₄] (968, bottom left (d)) and {[Me₄N]₄[(Ge₄S₁₀)Cu₄Mo₂S₈]}_n (995, bottom right (f)). Hydrogen atoms and counterions, if present, are omitted for clarity.

A previously discussed Cr/O adamantane-type cluster with hpdta ligands can be obtained as Ba linked chains in [Ba(OH₂)₅{Cr₄(OH)₄(hpdta)₂}]_n (943) by adding BaCl₂ to the initial reaction mixture without ethane-1,2-diamine.¹¹⁹ This leads to two parallel cluster strands connected via interactions between Ba ions and the organic ligand.

The only known group 7 example is the thiolate network [Mn₄(SPh)₈]_n (944, Fig. 21), in which all metal centers coordinate to the next cluster via a bridging thiolate, a composition often observed for transition metal chalcogenolates.⁵³⁴ It is isolated after a reaction of [Mn{N(SiMe₃)₂}₂]₂ with HSPh in THF at low temperatures.

A layered network of [{Cu₄{SC(NH₂)₂}₆}₂{SC(NH₂)₂}₃]_n(SO₄)₄ (945) can be observed from dissolving Cu₂SO₄ in sulfuric acid in the presence of thiourea.¹⁸⁷ Only three copper atoms per cluster carry a thiourea ligand forming the cluster sheets, while the last one only forms bonds within the adamantane-type scaffold.

Utilizing a multidentate thiolate ligand 4,5-dimercapto-1,3-dithiole-2-thionato (dmit) in a reaction with [Cu(MeCN)₄][ClO₄] an ammonium or pyridinium counterion form the dimeric anion in [{Cu₄(dmit)₃}₂]_n²⁻ (in 946–947), which is made up of layers facilitated by further Cu–S and S–S interactions.

The structural motif of a μ₃-Cu coordinating a six membered ring in an adamantane-type structure has been discussed several times before. Such a motif can also be found in a one dimensional zigzag chain polymer [(μ₃-Cu)Cu₄(SePh)₆(CuPPh₃)₃(4,4′-bipy)]_n (948, Fig. 21), in which such adamantanes are connected by 4,4′-bipy(CuPPh₃)₂ units to two Se atoms in the E position and another 4,4′-bipy terminally connected to an adamantane Cu moity.⁵³⁵ It forms from Cu(MeCOO), PhSeSiMe₃, PPh₃ and 4,4′-bipy.

Another dmit linked layered cluster exists in {[Et₄N][(Ag₄(dmit)₃]dmf}_n (949), in which a porous architecture filled with both cations and solvents is formed.

Linear chains of [Zn₄(SPh)₆] adamantane-type clusters are found in a series of compounds [(Zn₄(SPh)₈ROH]_n (950–953, R = Me, Et, ⁿPr, ⁿBu) obtained from ZnCO₃ and HSPh reacted in alcoholic solutions.⁵³⁶ Two opposing Zn atoms carry SPh ligands bridging to the next cluster to form the polymer, while the others carry a terminal alcohol or SPh ligand respectively which form hydrogen bonds to extend the structure to loose layers. There are a couple of related one dimensional adamantane-type clusters connected via organic ligands [(Zn₄(SPh)₈L]_n (954–955, L = trans-1,2-bis(4-pyridyl)ethylene, 4,4′-bipy).⁵³⁷ The first one forms a zigzag chain, while the second exhibits a helical buildup. They both are obtained from solvothermal reactions in water with HSPh, Zn(MeCOO)₂ and the appropriate ligand.

In the cadmium thiolate cluster network [(Cd₄(SPh)₈]_n (956), all Cd moieties carry bridging thiolate ligands to form a three dimensional architechture with helical arrangement of the adamantane-type clusters similar to that in cristobalite.⁵³⁸ This is obtained by reacting Ca(NO₃)₂ with HSPh and NEt₃ in ethanol. An alternative reaction strategy is the poylmerisation of 447 in THF/MeCN at elevated temperatures.²³² The same structural motif, albeit in a different crystallographic space group, is found for the para-fluorinated species [(Cd₄(SC₆H₄F-4)₈]_n (957).⁵³⁹

When exchanging the fluorine with Br or Me groups, the structure of the product varies significantly. The methylated species also forms a three-dimensional network, but arranges in cyclic groups of 4, 6 or 8 clusters, resulting in a porous zeolite like buildup. The bromide congener forms a layered structure [{Cd₆(SC₆H₄Br-4)₁₅}(CdSC₆H₄Br-4){Cd(dmf)₃}]_n (958) and incorporates solvent molecules in its buildup. This leads to two distinct clusters, each with three cadmium atoms linking to the next cluster via briding thiolate units, but also each with one terminally coordinated metal center, either by a thiolate or three dmf molecules. The chlorinated species has been synthesized as well, but could not be elucidated crystallographically due to a fast decomposition of the crystals.

956 can be partially decomposed to chains of [(Cd₄(SPh)₈PPh₃]_n (959) by the addition of PPh₃.²³²

The higher homolog [(Cd₄(SePh)₈]_n (960) is isostructural to its thiolate compound and prepared in the same manner by creating the selenolate and reacting with a Cd salt, CdCl₂ in this case.⁵⁴⁰

Using two Cd sources, (PhSe)₂Cd and CdX (Cl, Br), and a coordinating ligand, PR₃, to stabilize intermediates leads to one dimensional chains of [Cd₄(PhSe)₇X(PR₃)]_n (961–962), where two Cd atoms in each cluster connect to the next via PhSe bridges and the others carry a PPh₃ or X ligand.^541,542

Four isostructural Hg species [Hg₄(PhSe)7(X)solv]_n (963–966, Fig. 21) with different (pseudo)halides (X) and solvent ligands were obtained by changing to the appropriate salt, solvent and stabilizing ligand.^543–545 This chemistry could also be translated to a Te congener [Hg₄(PhTe)₇IPy]_n (967), although in this case, (PhTe)₂Hg was used alongside CdI₂ instead of the mercury halide, which did not lead to the inclusion of Cd into the final compound.⁵⁴⁶

For the group 13/16 combination, some In/Se networks are known. (C₅H₅NH₂)₂₄[In₂₈Se₅₄(H₂O)₄] (968, Fig. 21), formed by the elements and piperidine in aqueous solution through Method B, features a three dimensional structure of corner condensed adamantane-type clusters with some indium sites coordinated by water molecules.⁵⁴⁷ These positions can be partially substituted by Bi atoms when adding Bi(NO₃)₃ to the reaction mixture, leading to a doped structure (969). Other linking modes are obtained for the three dimensional network [μ₃-Se₄]_3.27[In_49.88Se_95.92](C₅H₁₂N)_26.0·(C₂H₈N)_42.4 (970), in which [In₄Se₁₀] clusters are linked by μ₃ Se and [InSe₄] fragments, a structure obtained from the elements in piperidine solvothermally.⁵⁴⁸ Adding 1,4-dioxane and 3,5-dimethylpyridine to the mixture changes the outcome to [In₄Se₁₀]·(C₇H₁₆N)_1.8·(C₂H₈N)_2.2 (971), comprising μ-Se₃ linkers between the individual clusters.

In group 14/16 adamantane-type clusters, extended structures are produced mainly by adding transition metal complexes to ammonium or alkaline metal salts of [Q₄E₁₀] clusters (972–994).^{260,263,272,275,281,549–552} By utilizing two different transition metal complexes during the synthesis, a more complex Cu₂MS₆ (M = Mo, W) linker between Ge/S adamantane-type compounds was obtained to form the MOF-like {[Me₄N]₄[(Ge₄S₁₀)Cu₄M₂S₈]}_n (995–996, Fig. 21).⁵⁵³ The concept could also be used to introduce another group 14 element, here tin, to Ge/S adamantanes by adding SnCl₂ to K+ or Cs+ salts of [Ge₄S₁₀]⁴⁻ in ionic liquids, with the exact outcome dependent on the ionic liquid used (997–999).^554,555 In one case, {[BMIm]₂[Ge₄Se₉]}_n (997), this approach did not lead to the incorporation of Sn into the structure.⁵⁵⁴

In another case, utilizing the functional ligand in 579, manganese complexes were used to form a coordination polymer forming a layered structure [Mn₂{(OOCC₂H₄Ge)₄S₆}(MeOH)(dmf)₂]_n (1000) by using the transition metal as a linker between the acid moieties.⁵⁵⁶

Most other transition metal linked adamantanes are isolated after reactions of simple binary or elemental precursors in solution (1001–1005)^{549,557–560} or, in one case, the solid state,⁵⁶¹ which results in clusters linked by disordered Cu_0.44Ge_0.56S₄ sites (in 1006).

Two examples also showcase the possibility of creating manganese linked adamantane-type structures by Method E, the extraction of a solid created from a melt of simple precursors (1007–1008).^275,282 This led to the only example of a tellurium adamantane in network structures (1007).

Pure group 14/16 structures can also be obtained, one of them containing the same polymeric chain [Ge₄Se₉]²⁻ previously discussed as the surprising outcome of a reaction of a Ge/S adamantane with SnCl₂. In this case, the compound {[Pr₂NH₂][PrEtNH₂][Ge₄S₉]}_n (1009) could be isolated from a solvothermal reaction of GeS₂ and [Pr₂NH₂]Cl in the presence of NaHCO₃.⁵⁶²

The other example {[Me₄N]₂[OSn₅Se₁₀]}_n (1010) consists of a corner condensed oxygen centered [μ₄-OSn₄Se₁₀] adamantane-type structure synthesized solvothermally from the elements and [Me₄N]OH.²⁷⁸

Aside from ionic or ligand decorated networks, partial acidic decomposition of 497 led to a novel modification of GeS₂, δ-GeS₂ (1011), with corner condensed Ge₄S₁₀ adamantanes, which can be derived from two interpenetrating cristobalite-like structures of γ-GeS₂.²⁶⁶

2.2. 1,3,5,7-Tetrasubstituted adamantane derivatives

In 1941, the first synthesis of adamantane (1012), the smallest so-called diamondoid,^565,566 was achieved by Prelog, yielding 1.5% from Meerwein's ester through a series of conventional enolate alkylation techniques, Wolff–Kishner reductions, and a final double decarboxylation step (Scheme 4).⁵⁶⁷ Subsequent refinements by Stetter increased the yield to 6.5%, but the method remained intricate, involving multiple stages for the removal of functional groups used in adamantane synthesis.⁵⁶⁸ In 1957, Paul von Ragué Schleyer introduced a groundbreaking Lewis acid-promoted rearrangement of tetrahydrodicyclopentadiene, offering an alternative pathway to adamantane synthesis. This isomerization method significantly enhanced the yield by approximately 40%.⁵⁶⁹

Scheme 4. Synthesis and functionalization of tetra-substituted adamantane.

These sections center on the synthesis of 1,3,5,7-tetra-substituted 1012 and explores its applications in advancing nonlinear optical properties.^570,571 In these sections, we employ two distinct approaches. The first approach concentrates on directly incorporating functional groups onto the adamantane core. The second approach delves into functional group transformations, commencing from 1,3,5,7-tetra-substituted adamantane as the starting point.

2.2.1. Direct functional group introduction

Adamantane, a tricyclic hydrocarbon comprised of interconnected chair cyclohexane rings, exhibits remarkable symmetry and inherent resistance to direct modification due to the absence of functional groups. Nevertheless, there exist several approaches to introduce functional groups into adamantane.^572,573 One such method involves reactions of adamantane with electrophiles such as bromine (Br₂). Subsequently, nucleophilic substitutions enlarge the spectrum of possible substituents; these reactions must exclusively procede through an S_N1 mechanism. Hence, this mechanism involves the reaction of tertiary adamantyl cations with nucleophiles. Notably, the nucleophilic C–H-bond substitution 1012 can be accomplished directly with strong acids such as hydrochloric acid (HCl) and hydrobromic acid (HBr).

In general, these conditions facilitate the abstraction of hydride ions while also serving as sources of nucleophilic species.

Direct bromination of 1012 leads to the formation of only 1-bromo adamantane.^574,575 However, the presence of Friedel–Crafts-type catalysts like AlCl₃ and AlBr₃ allows for the gradual replacement of more tertiary C–H bonds with bromine. The successful synthesis of 1,3,5,7-tetrabromoadamantane (1013) has been achieved by utilizing AlCl₃ and Br₂ at 150 °C (Scheme 5).^576,577 Note that the use of larger amounts of AlCl₃ leads to the generation of not only 1013 but also small amounts of 1-chloro-3,5,7-tribromoadamantane in around 12% yield. In addition, synthesis of 1013 has been achieved in the presence of AlBr₃ under sealed tube conditions at 150 °C. This approach avoids halogen exchange during the synthesis of 1013 by utilizing aluminum tribromide.⁵⁷⁸ The use of two equivalents of AlBr₃ resulted in the clean formation of 1013 with 85% yield at room temperature.⁵⁷⁹ The established one-step method to synthesize 1,3,5,7-tetrachloroadamantane (1014) proceeds by refluxing adamantane in CCl₄ in the presence of AlCl₃ (Scheme 5).⁵⁸⁰

Scheme 5. Direct tetra-functionalization of adamantane.

Direct methylation of 1012 with tetramethylsilane as the methylation agent and a Friedel–Crafts catalyst has been explored and optimized for the synthesis of 1,3,5,7-tetramethyladamantane (1015, Scheme 5). With the introduction of four methyl groups in the presence of AlCl₃, adamantane underwent fourfold methylation of all bridgehead carbons.⁵⁸¹

As is well known, Friedel–Crafts alkylations can generate mixtures of substitution products, and the selective introduction of aryl groups at the 1,3,5,7-positions of 1012 requires precise control of reaction conditions.

In 1968, Stetter and Krause employed a two-step process to add phenyl groups to the adamantane molecule, resulting in the synthesis of 1,3,5,7-tetraphenyladamantane (1016, Scheme 5). Initially, they brominated adamantane using molecular bromine (Br₂). Subsequently, in the presence of AlCl₃ and benzene, phenyl groups were introduced via Friedel–Crafts alkylation.⁵⁸²

In 1972, Newman utilized the Friedel–Crafts catalyst along with tert-butyl bromide to synthesize 1016 from 1-bromoadamantane. This method allowed for selective Friedel–Crafts phenylation under controlled reaction conditions, resulting in the clean formation of 1016.⁵⁸³

Alternatively, 1016 was synthesized from adamantane under refluxing conditions, utilizing a catalytic amount of AlCl₃. The reaction proceeded overnight giving a yield of 89%.⁵⁸⁴ Furthermore, 1012 can be directly converted into 1,3,5,7-tetrahydroxyadamantane (1017) under remarkably mild conditions, employing an excess of methyl(trifluoromethyl)dioxirane in solution (Scheme 5).⁵⁸⁵

Recently, we reported a new meta-selective adamantane tetraarylation using substituted benzenes. This Friedel–Crafts-type reaction yields a large amount of all-meta-tetrafluorophenyl adamantane derivatives (1018–1021) in the presence of tert-BuBr as the additive and AlCl₃ as the catalyst (Scheme 6).⁵⁸⁶

Scheme 6. Direct meta-substituted tetra-functionalization of adamantane.

2.2.2. Functional group transformations

Functional group transformations in organic synthesis are a fundamental and essential aspect of modern organic chemistry.^587,588 Functional groups attached to adamantane derivatives can be modified to create a wide range of compounds with tailored properties. This field of study is at the core of organic synthesis, and plays a crucial role in designing and preparing complex adamantane derivatives for various applications, including materials science,^589–591 pharmaceuticals,^592,593 and agrochemicals.⁵⁹⁴ Functional group transformations involve converting one functional group into another while preserving the overall molecular structure, such as the adamantane core.^{565,569,595–597} Developing efficient and selective methods for functional group transformations encompasses a wide array of chemical reactions. These reactions can include substitution,^598–601 addition,⁶⁰² and elimination reactions,^603–605 among others. They are applicable to various functional groups, including halides, alcohols, ketones, and carboxylic acids, among others. The choice of transformation method depends on the specific functional group and the desired product.

The conversion of 1,3,5,7-tetracyanoadamantane (1022, Scheme 7) from 1013 was achieved through a nucleophilic radical substitution reaction. Interestingly, no reaction occurred in the dark. However, upon photolysis with sodium cyanide in DMSO in a quartz vessel using a Rayonet reactor, a mixture was obtained where 1022 was the dominant product.⁵⁷⁹ The synthesis of 1,3,5,7-tetraiodoadamantane (1023) did not proceed directly from 1012. Initially, a bromination reaction was conducted to substitute hydrogen atoms on the adamantane bridgeheads with bromine atoms. This process involves halogen exchange in the presence of methyliodide, aluminum powder, and bromine, carried out at 80–85 °C for 45 min, as illustrated in Scheme 7.⁶⁰⁶ An improved procedure for 1023 involves the use of methyliodide and AlBr₃, resulting in a yield of 91% (Scheme 7).⁵⁷⁹

Scheme 7. Functional Group transformations from 1,3,5,7-tetrabromoadamantane.

The direct method to prepare 1,3,5,7-tetrahydroxyadamantane (1017) from 1012 utilizes a strong oxidation reagent such as dioxiranes, which poses a risk of explosion during their preparation (see Scheme 5). Target compound 1017 can be prepared conveniently from 1013 in the presence of concentrated H₂SO₄ and Ag₂SO₄.⁵⁸² Exhaustive Soxhlet extraction improved the yield, increasing it to 98% compared to the 84% reported in the literature.⁶⁰⁷ Starting from 1013, the synthesis of 1,3,5,7-tetrakis(1,3-dibromophenyl)adamantane (1024) can be accomplished with 1,3-dibromobenzene and AlCl₃ (Scheme 7).⁶⁰⁸

The nitration of 1012 with concentrated nitric acid in glacial acetic acid at elevated temperatures has been previously reported to yield 1-nitro-, 1,3-dinitro-, and 1,3,5-trinitroadamantanes, albeit in moderate to low yields.⁶⁰⁹ When adamantanes are subjected to nitration with nitrogen dioxide at elevated temperatures, the primary products are typically 1-nitro and 1,3-dinitro derivatives. Similarly, the photochemical reaction of N₂O₅ with 1012 primarily results in mononitration. Note that while the oxidation of tert-alkyl amines to their corresponding nitro compounds is a standard method, it has not been widely used in the past to prepare compounds containing more than two nitro groups. In a noteworthy synthesis, Sollot and Gilbert reported the hydrolysis of 1,3,5,7-tetraaminoadamantane·tetrahydrochloride (1025) to obtain the free tetraamine, which was subsequently oxidized using permanganate to yield the desired 1,3,5,7-tetranitrodamantane (1026) with a yield of 45% (Scheme 8).⁵⁷⁶Additionally, the powerful oxidizing agent dimethyldioxirane was employed to synthesize 1026, achieving an impressive yield of 91%.⁶⁰⁶

Scheme 8. Synthesis of 1,3,5,7-tetranitroadamantane.

The reduction of 1022 was accomplished using monochloroborane-methyl sulfide in refluxing THF. Subsequent reaction with dry methanolic HCl resulted in the formation of 1,3,5,7-tetrakis(aminomethyl)adamantane tetrahydrochloride with an impressive yield of 98%. To obtain the 1,3,5,7-tetrakis(aminomethyl)adamantane (1027), deprotonation of an aqueous solution with NaOH was performed (Scheme 9).⁵⁷⁹ Additionally, hydrolysis of 1022 led to 1,3,5,7-tetracarboxylic acid adamantane (1028). This method serves as an excellent alternative for preparing 1028, reducing the number of synthetic steps compared to those reported by others (Scheme 9).⁶¹⁰

Scheme 9. Functional Group transformations from 1,3,5,7-tetracynoadamantane.

The use of ‘click chemistry,’ specifically tetrazole formation through the cycloaddition of azides to nitriles in the presence of ZnCl₂, offers an especially cost-effective route to obtain tetrakis-tetrazole derivatives of adamantane. When applied to 1022, this process exhibited slightly slower kinetics compared to aromatic or unhindered aliphatic nitriles but ultimately yielded 1,3,5,7-tetrakis(tetrazol-5-yl)adamantane (1029, Scheme 9). The reaction can be conducted in DMF under reflux conditions for 48 h or at 175 °C in an autoclave within 6 h. The former conditions provide a purer product.⁶¹¹

The synthesis of 1,3,5,7-tetra(diphenylphosphate)adamantane (1030) with a yield of 62% can be achieved by reacting 1,3,5,7-tetrahydroxyadamantane (1017) with diphenyl chlorophosphate under controlled conditions (Scheme 10).⁶¹² Introduction of electron-rich arenes (substituted anisoles) to 1,3,5,7-tetrahydroxyadamantane through Friedel–Crafts alkylation results in symmetrical tetraaryladamantanes with yields ranging from 20–41% (1031–1034, Scheme 10). This alkylation process requires strong Brønsted acids, such as tosylic acid (TfOH), and elevated temperatures. The study reports that weaker acids or lower temperatures are ineffective, leading to low reactivity and consequently very low yields.^{607,613–615}

Scheme 10. Functional group transformations from 1,3,5,7-tetrahydroxyadamantane.

In this context, various functional groups were introduced onto the phenyl rings of 1016 through electrophilic substitution at the para-positions of the phenyl moieties, as outlined in Table 22. The direct functionalization of 1016 through electrophilic aromatic substitution can serve as a good starting point for synthetic modifications, enabling access to a wide array of functional groups (R) attached to the aromatic moieties of 1,3,5,7-tetraaryladamantanes (R = Br, I, SO₂Cl, NO₂, COCH₃, and CHO).

The bromination of 1016 in liquid bromine selectively occurs at the para-position, yielding 1,3,5,7-tetrakis(4-bromophenyl)adamantane (1035, Table 22) with 60% yield, without the need for additional catalysts.⁶¹⁶ However, when bromination of 1016 is conducted in the presence of Fe, 1035 is obtained in a significantly improved yield of 94%,⁶¹⁷ which further increases to 96% at elevated temperatures.⁶¹⁸ The iodination of 1016, using PhI(OCOCF₃)₂ in a chloroform solution of iodine, leads to the formation of 1,3,5,7-tetrakis(4-iodophenyl)adamantane (1036, Table 22).⁶¹⁹ The sulfonation of 1016 using chlorosulfuric acid efficiently produces 1,3,5,7-tetra(phenyl-4-sulfonyl chloride)adamantane (1037) with a yield of 57% (Table 22).⁶²⁰ Starting material 1016 was subjected to nitration in fuming nitric acid at −15 °C for 30 min, yielding 1038 in low yield (Table 22). The degree of nitration can be controlled by adjusting the reaction time.^621,622 The Friedel–Crafts acetylation of 1016 results in the formation of 1039 with good yield (Table 22). Additionally, 1,3,5,7-tetrakis-4-formylphenyladamantane (1039)⁶²⁶ was synthesized using a modified patented procedure involving the titanium tetrachloride-promoted formylation of 1040 (Table 22).⁶²³

The synthesis of 1041 was achieved by reacting 1036 with NaOMe and Cu(i)Br in dry MeOH/DMF, yielding a 47% yield. Similarly, the reaction of 1,3,5,7-tetrakis(4-bromophenyl)adamantane (1035) with NaOMe and Cu(i)Br in dry MeOH/DMF results in the formation of 1041 with a yield of 52% (tableref>/tableref>).⁶¹⁴

The synthesis of 1,3,5,7-tetrakis(4-cyanophenyl)adamantane (1042) commenced with 1036, using the Rosenmund–von Braun reaction. Typically, in the literature, ethane-1,2-diamine is used to eliminate the nitrile–copper cyanide complexes and is followed by nitrile extraction to obtain the desired product.^592,624 However, in this particular case, ethane-1,2-diamine proved to be inefficient, and the use of an excess of aqueous KCN was found to be more effective in the synthesis of 1042 (Table 23).⁶²⁵

1,3,5,7-Tetrakis(4-phosphonatophenyl)adamantane (1043), was synthesized through a two-step process but without isolating the intermediate. First, a palladium-catalyzed P–C coupling reaction between 1036 and diethylphosphite was carried out. Subsequently, the resulting phosphonic acid diethyl ester was subjected to acidic hydrolysis to obtain 1043 (Table 23).⁶²⁷

A copper(i)-catalyzed coupling reaction was employed to synthesize various derivatives of 1044–1049 (Table 23). This reaction involved the use of pyrrole, carbazole, imidazole, benzimidazole, phenylimidazole, and 2-CH₃-imidazole as reactants. The reaction took place in the presence of N,N-dimethylglycine and DMSO at a temperature of 120 °C for a duration of 5 days.^628,629

The synthesis of 4,4′,4′′,4′′′–(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-bis(4-methoxyphenyl)aniline) (1050) was achieved by combining bis(4-methoxyphenyl)amine and 1036 in solution in the presence of Pd(OAc)₂, t-Bu₃P, and t-BuOK (Table 23).⁶³⁰ The reaction of 1036 with phenyl boronic acid under Suzuki coupling conditions yielded compound 1051 (Table 23). This compound is soluble in CHCl₃, making it easy to purify and characterize.⁶¹⁹ It can readily be converted to 1,3,5,7-tetrakis(4-trimethylsilyl-ethynylphenyl)adamantane by reacting it with Et₃N, trimethylsilylacetylene, Pd(PPh₃)₂Cl₂, and CuI in toluene. The crude product can then be deprotected to give 1,3,5,7-tetrakis(4-ethynylphenyl)adamantane (1052) in a yield of 74% (Table 23).⁶²¹ This product was also prepared by a palladium/copper co-catalytic system for coupling 1036 with Me₃Si-ethynyl in the presence of Et₃N and DMSO.^621,631

Oxidation of 1036 by conventional methods with peracetic acid (30% H₂O₂ and acetic anhydride), sodium perborate (NaBO₃·nH₂O) in acetic acid, or sodium periodate (NaIO₄) unexpectedly gave 1,3,5,7-tetrakis[4-(diacetoxyiodo)phenyl]adamantane (1053) in low yield, accompanied by poorly soluble and unidentifiable polymeric products (Table 23). After further investigations, it was finally possible to synthesize 1053 in 97% yield by using MCPBA in CH₂Cl₂/AcOH (1 : 1) under dilute conditions.⁶³³ The synthesis of 1,3,5,7-tetrakis(4-stilbenylphenyl)adamantane (1054) is readily achieved by reacting compound 1036 with excess styrene under palladium-mediated Heck coupling conditions, resulting in an 86% yield. However, when starting with 1,3,5,7-tetrakis(4-bromophenyl)adamantane (1035) under analogous conditions, consistently lower yields were obtained.⁶³⁴

3. Optical properties: linear optical phenomena and photocurrent conversion

Compounds with an adamantane-type scaffold have most commonly been investigated for their luminescence properties over the years. Especially molecules with group 16 or group 17 elements in the E position have been the focus of such investigations, but other emissive examples have been reported as well.

Compounds containing the highly distorted group 11 chalcogenide adamantane cations [(ER)₄M₆{(Ph₂P)₂R}₄]²⁺ (848–853, 855–857) have been investigated systematically for their photoluminescence behavior.^493,494,496 While the emission of the copper complexes [(SePh)₄Cu₆{(Ph₂P)₂R}₄][BF₄]₂ (848–849, R = CH₂, NH) in solution was of low intensity when compared to other related copper clusters, the long lifetime of the excited state suggests a spin-forbidden transition likely stemming from a ligand-to-metal charge transfer between the PhSe fragments and the Cu centers.⁴⁹³ Most silver congeners only feature a significant luminescence at low temperatures of about 77 K in the solid state, which consists of a single emission peak for [(ER)₄Ag₆{(Ph₂P)₂Me}₄][PF₆]₂ (850–853, ER = SPh, SC₆H₄Me-p, SePh, SeC₆H₄Cl-p) at around 700 nm. With a rising electron richness of the ER fragments from 850 to 853, the signal shifts to higher energies (746 nm to 666 nm). This was attributed to the influence of the π-acceptor ability of the ER moiety, which affects the orbital splitting of the bonding and antibonding orbitals.⁴⁹⁴ In contrast, compounds 856–857 show a double emission at 77 K, while 855 is non-emissive.⁴⁹⁶ An explanation of the different behaviors of the silver homologs is still elusive.

The Cu-thiolate adamantane moieties in [(NEt₄]₄[(SPh)₄(CuX)₆] (846–847, X = Cl, Br) show a more symmetrical buildup and a strong photoluminescence with a single emission at around 560 nm.¹⁷⁰

[Et₄N]₂[Cu₄(SPh)₆] (256), comprising an inverted adamantane-type core as compared to 846 and 847, shows a much weaker photoluminescence when being excited at 350 nm, but exhibits a dual emission at 436 nm and 573 nm, which is attributed to ligand-to-metal charge transfer or transitions between the metal centers, respectively, which has not been possible for the previously discussed compounds due to their larger Cu⋯Cu distances.¹⁷⁰

As part of a study on differently sized Cd-selenolate supertetrahedra, the photoluminescence of [ⁿPr₄N]₂[(CdCl)₄(SePh)₆] (409) was discussed.²²⁸ Significant emission is only detected at temperatures below ∼50 K and is attributed to forbidden transitions. Other adamantane-type thiolate clusters featuring ammonium counterions, like [Me₄N]₂[(CdSPh)₄(SPh)₆] (311) and [Et₃NH]₂[(CdSC₆H₄-4-Me)₄(SC₆H₄-4-Me)₆] (318), exhibit photoluminescence at room temperature, with low to moderate intensity.^219,221

Group 12 chalcogenolate adamantane anions also have been subject to studies in combination with the chromophore cation DAMS. The clusters were found to affect the intramolecular charge transfer and reduce quenching.²¹¹

The cadmium cluster (DAMS)₂[(CdSPh)₄(SPh)₆] (313) and its iodine derivative (DAMS)₂[(CdI)₄(SPh)₆] (414) have been proven to show significant photoluminescence at room temperature.²¹⁸ While (DAMS)I already exhibits an emission under similar conditions, 313 and especially 414 do so much more intensely, albeit slightly blue-shifted. Additionally, two-photon pumped lasing spectra revealed nonlinear optical properties for both compounds.

The first OLED constructed from such a compound comprises (DAMS)₂[(ZnSPh)₄(SPh)₆] (302), which follows the trend of a more intense and slightly blue-shifted emission as compared to the pure chromophore.²¹¹ The device produces a narrow red emission at 630 nm with a full width at half heights of the measured peak of 80 nm.

Subsequently, combinations of adamantane anions and different chromophore cations were explored. In [Ru(phen)₃][(CdSPh)₄(SPh)₆] (314), the fluorescence enhancing findings made for DAMS compounds could be repeated in a titration study, where an increase of the fluorescence intensity could be observed when adding cluster anions to a solution of the ruthenium complex.²¹⁹ This effect reaches a plateau at a 1 : 1 ratio, which is in accordance with an anion–cation charge transfer indicated by both spectroscopic findings and theoretical studies.

The cluster-dye composite [Ru(2,2′-bipy)₃][(ZnSPh)₄(SPh)₆] (303) was investigated for its photocurrent conversion behavior, which can be enhanced by substituting the adamantane type cluster with larger supertetrahedra.²¹²

The earlier UV-vis measurements on group 14/16 adamantane anions without organic ligands revealed the intra molecular transitions to be responsible for the absorption behavior, with no or only negligible contributions of the counterions in case of ammonium cations.^{279,281,284,286} The optical properties of the adamantane-type cluster remain dominant even in the presence of some transition metal complexes, as long as no charge transfer between them is possible.^{295,296,298,300} Therefore, such charge transfer pathways have to be present to influence the band gap more significantly, as has been seen in [Ni(trien)₂]₂[Ge₄S₁₀] (552).^{288–291,294} In the case of [Me₂Vio]₂[Ge₄S₁₀] (544), fluorescence can be detected distinctly red-shifted from the fluorescence of [Me₂Vio]I₂ by the charge transfer between the cation and anion. The cluster compound also shows solid-state solvatochromicity, depending on the inclusion of water or MeOH into the crystal structure, and it is photoelectrically active.²⁸⁹ A similar behavior in regard to fluorescence and photocurrent was found for [DMBPE]₂[Ge₄S₁₀] (546) and for the compounds [(C_nH_2n+1)₂Vio]₂[Ge₄S₁₀] (540–543, n = 0, 2, 3,4).^288,291 By utilizing a porphyrin derivative as counterion, like in the fluorescing species TMPyP[Ge₄S₁₀] (545), even larger photocurrents could be measured.²⁹⁰ Lastly, there are cases, in which the anion plays nearly no role in the transitions at the band gap, such as in [Ni₂(μ-teta)(teta)₂][Ge₄S₁₀] (555), in which the photoluminescence does not deviate much from the one found for the amine hydrochloride.^293,297,299 Similar to 544, [Ni(phen)₃]₂[Ge₄S₁₀] (550) additionally features the ability to reversibly change its color depending on the inclusion of water or MeOH in its crystal structure (Fig. 22).²⁹³

Fig. 22. Solvatochromicity in [Ni(phen)₃]₂[Ge₄S₁₀] (550), depending on the inclusion of H₂O (red curve) or MeOH (blue curve) into the crystal lattice. (reproduced from ref. 293 with permission from ACS).

For [Ni(teta)(en)][Ni(teta)(hda)][Sn₄Se₁₀] (558) moderately weak photocurrent photoelectric conversion was observed.²⁹⁹

An extensive study of lanthanide complexes of the 3-NO₂Tp ligand features adamantane type clusters in [(μ₄-O){M(3-NO₂Tp)}₄(μ₂-OMe)₆] (665–670), with the photoluminescence behavior depending heavily on the lanthanide center.³⁶⁷

The Yb cluster 671 also shows photoluminescence when excited at 405 nm with an emission pattern in the near infrared region, as typical for Yb³⁺ complexes.³⁶⁸

The mixed-metal compounds [(μ₃-M)(CdPPh₃)(MPPh₃)₃(TePh)₃(μ₃-TePh)₃] (903–904, M = Cu, Ag) show strong photoluminescence at around 480 nm when excited at 350 nm. This was assigned to transitions between the coinage metal and its ligands, rather then involving the Cd centers.⁵¹⁶ The spectrum of 903 shows an additional shoulder attributed to intracopper ds/dp transitions owing to the small Cu⋯Cu distances.

Adamantane-type clusters with a group 17 element in E position are the second group that were heavily investigated for their optical properties, chiefly among them the copper halide anions [Cu₄E₆]²⁻. The first bromine congener investigated was [{Cu(Hdabco)}₄Br₆](HCOO)₂ (817), although a cationic one due to the ligands at the Cu sites. It showed strong photoluminescence with a yellow emission at 556 nm.⁴⁶⁸ Thermochromic photoluminescence can be observed for (H₂dpipa)₃[Cu₄Br₆][Cu₂Br₆] (815), with different bromido cuprate anions in its structure, and its Cl homolog, which was extensively studied by DFT calculations.^459,467 The luminescence of [ⁱPr₄N]₂[Cu₄Br₆] (809) and [^tBu₃NMe]₂[Cu₄Br₆] (812) was compared to other copper bromide compounds, and 809 was found to feature the most brilliant red-orange emission, which was utilized to manufacture a white-light emitting LED in conjunction with two other commercial phosphors.⁴⁶¹

The combination of bromido cuprate anions, [Cu₄Br₆]²⁻ among them, and a polyoxotitanium cluster in a series of compounds including [Ti₁₂(μ₃-O)₁₄(OⁱPr)₁₈][Cu₄Br₆] (816) showed a vast dependency of the absorption spectra on the anion and the resulting supersalt structure.⁴⁶⁶

Also [Cu₄I₆]²⁻-containing compounds have been investigated for their luminescence properties in several studies.^{471,472,474,476,477} [Mn(tdpmO₃)₂][Cu₄I₆] (828) and [Mn(dppbO₂)₃]₂[Cu₄I₆][Cu₂I₄] (829) are part of a series of dual-emission compounds with both the cation and anion showing a distinct emission (Fig. 23).⁴⁷⁷ When grinding crystals of 829, a triboluminescence originating from the same centers as the photoluminescence is detectable.

Fig. 23. Photoluminescence at different temperatures of 828 (left, reproduced from ref. 477 with permission from ACS) and 829 (right, reproduced from ref. 477 with permission from ACS).

The band gap in compounds with a [μ₄-O(CuR)₄Cl₆] inorganic core is determined by ligand to metal charge transfer and therefore heavily influenced by the ligand used, but such compounds do not show luminescence as opposed to their anionic relatives.^390,403,415

4. Optical properties: nonlinear white-light generation (WLG) and second-harmonic generation (SHG)

The huge compositional variety of adamantane based clusters offers the possibility to finely tune the optical properties for a multitude of applications. Obviously, the fundamental element of all optical properties is defined by the HOMO–LUMO gap, in the case of adamantane (1012), this gap is ∼6.49 eV.⁶³⁵ As a consequence, the absorption onset and corresponding photoluminescence is in the ultra-violet (UV) spectral range.⁶³⁵ An advantage of this large HOMO–LUMO gap is a very high photostability of adamantane, since it is virtually unaffected by light in the visible spectral range.⁶³⁶ At the same time, the large HOMO–LUMO gap makes it difficult to make use of pure adamantane in optoelectronic applications. However, by functionalization on both the Q and E site, the HOMO–LUMO gap can easily be tuned. Functionalization schemes include fluorination, addition of alkali-metals or introduction of very simple or complex organic ligands, only to name a few.^637–640 Even with these rather simple functionalization schemes, it is already possible to tune the HOMO–LUMO gap and thus the optical properties of fully organic adamantanes to cover virtually the whole visible spectral range.

An even larger space for tuning the optical properties opens up when stepping away from the fully organic adamantane by alternating the composition on the Q- and E-site too.

In the last decade, several hundreds of adamantane based clusters have been investigated theoretically.⁵⁷¹ All the structures with adamantane like cores and the same ligand field show a variation in the HOMO–LUMO gaps in a range of about ΔE ≈ 2 eV. This is demonstrated in Fig. 24 for clusters with homogeneous phenyl ligands (tetraphenyl clusters) and different cluster cores. It should be noted that Fig. 24 is not exhaustive and only features a relatively small sample of possible modifications of the core which have been investigated recently.

Fig. 24. HOMO–LUMO energy gaps calculated within the density functional theory in the independent particle approximation for selected adamantane-based tetraphenyl clusters.

The highest HOMO–LUMO gap is predicted (DFT calculations in the IPA) for the prototypical AdPh₄ cluster (1016, E_g ≈ 4.65 eV). Modifications of the adamantane core (inorganic and/or heterogeneous composition) lower this value up to about 2 eV, with a minimum value calculated for the heterogeneous and inorganic [PhSi{CH₂Sn(Te)Ph}₃] (891) cluster. Interestingly, a fine tuning of the HOMO–LUMO gap value can be achieved by the gradual modification of the cluster core, as shown exemplarily by the stepwise transition from the inorganic [(PhSi)₄S₆] cluster (568) to the organic [(PhC)₄S₆] cluster.⁶⁴¹ The first substitution largely modifies the HOMO–LUMO-gap, due to an abrupt modification of the bond lengths in the core. For the subsequent modifications, a quite gradual change is seen (as shown in Fig. 24). The fine tuning of the HOMO–LUMO gap is also expected for the stepwise transition between the other cores and has consequences for the manipulation of the optical response.

In addition to tuneability of the linear optical properties, it was found that a large number of cluster molecules of adamantane-type cluster compounds with composition [(RQ)₄E₆] presented in Table 13, with group 14 elements in the Q position and those of group 16 in the E-position, show strong nonlinear optical properties when they are irradiated by a simple near-infrared (NIR) low-power laser diode.^310,320 This nonlinear response manifests itself in the emission of light covering virtually the whole visible spectrum from ∼400 nm to 800 nm (see Fig. 25 for emission spectra under various excitation energies with excitation region marked by dotted grey line). Because of the broad spectral-range, we will refer to the process as white-light emission, although due to the spectral intensity distribution the appearance to the human-eye is warm-white (see Fig. 25).

Fig. 25. Broad white-light emission of [(StySn)₄S₆] (598), shown in differently colored lines for various excitation wavelength (indicated by the grey dotted part of the spectra) in the range of 700–1050 nm (left). Photograph of the emission of [(StySn)₄S₆] sandwiched between two glass slides and excited with 800 nm laser light (reproduced from ref. 320 with permission from AAAS).

As it has been demonstrated that the nonlinear optical response of the clusters can be generally interpreted in terms of multiphoton processes,^309,642,643 tuning the HOMO–LUMO gap makes it possible to tune the nonlinear response too, e.g., the frequency dependence of the main SHG and THG peaks. It is worth mentioning here that SHG can be observed on these materials even for compounds that crystallize in centrosymmetric space groups, which usually is an exclusion rule, as only crystals lacking inversion symmetry can produce bulk SHG. However, the SHG in such samples appears to be due to surface effects and/or defects in the crystal. With the SHG being very effective, the contribution of the surfaces of the (micro- or nanosized) crystals is sufficiently high to observe SHG in most cases.

The optical response of a wide class of adamantane-based clusters and cluster aggregates has been calculated from first principles in recent years.^{309,571,642–645} The calculations show that all adamantane-based clusters are characterized by a nonlinear optical response with the same structure, as long as they have the same ligand field. For example, a prominent peak above 2 eV followed by a dip and a second peak is common to all adamantane-based cores with phenyl ligands. This suggests that the nonlinear optical response is dominantly defined by the ligand structures and originates only to a minor extent in the core region. This is demonstrated exemplarily in Fig. 26, where we compare the SHG signal of AdPh₄ (1016) with that calculated on the same footing for CPh₄.⁶⁴⁶

Fig. 26. Second-harmonic generation (average of all tensor components, absolute values) calculated as a function of the incident laser wavelength for the isolated [AdPh₄] cluster (1016) (blue line) and the [CPh₄] cluster (orange line) within the independent particle approximation at the DFT equilibrium geometry.⁶⁴⁶.

The structure of the second order nonlinear response is basically the same for the two clusters, although CPh₄ has no adamantane core at all. This, however, does not mean that the cluster core does not affect the linear and nonlinear optical properties. As we will discuss in the following, the geometry and the chemistry of the core have an impact on the magnitude of the nonlinearities and, to a lesser extent, to their spectral position. Thus, modifications of the cluster core offer the possibility to manipulate the optical response towards desired energies and intensities. Yet, the main characteristics are preserved as long as the ligand structures are maintained.

Although the nonlinear optical response originates in and is dominated by the ligand field, as previously discussed, the optical nonlinearities are enhanced by disorder and structural asymmetry in the cluster core. This is particularly true for molecules featuring a heterogeneous core composition.⁶⁴² This is clearly shown with clusters [PhSi{CH₂Sn(E)Ph}₃] (889–891, E = S, Se, Te) as a model system. The cluster structure is shown in Fig. 27, along with the distortion in the core, quantified by the ratio between the largest and shortest bond length. The core symmetry is greatly reduced from S to Te, while the optical susceptibilities are correspondingly enhanced, as displayed in Fig. 28. The AdPh₄ cluster features a regular core and has the lowest SHG coefficients. This effect is quite remarkable, as a range of intensities spanning an entire magnitude of SHG responses can be achieved with these structures. Noticeably, the form of the second order optical response typical for tetraphenyl compounds (displaying a main peak above 2 eV, followed by a dip and a second peak) is maintained for all variations of the core.

Fig. 27. Atomic structure calculated within DFT in the independent particle approximation for AdPh₄ (1016, top left) and different tetraphenyl clusters with modified cluster cores. The circle color corresponds to the respective line color of the second order optical response shown in Fig. 28.^642,644.

Fig. 28. Second-harmonic generation per cluster (the average of all tensor components is shown) calculated within DFT in the independent particle approximation for different tetraphenyl clusters with modified cluster cores.^642,644.

Although a generally accepted theory of the observed white-light generation is still missing, it is known that higher order nonlinear effects like supercontinuum generation involve the whole catalogue of nonlinear-optical effects, which add up to produce emission with an extremely broad spectrum.^646–648 These nonlinear effects include self- and cross-phase modulation, four-wave mixing, and many others, for which an exhaustive theory is still missing. Nevertheless, it is reasonable to assume that a more or less high nonlinear optical activity is a prerequisite for the mentioned effects leading to white-light emission. In this respect, the theoretical studies performed in the last years allowed for an (at least partial) understanding of the optical response of the white-light emitters and revealed several interesting aspects. As a general feature, all clusters showing WLE are characterized by strong optical nonlinearities of second and third order, at least as strong as that of the crystalline ferroelectrics.^{309,571,642–646,650,651} The optical nonlinearities feature high peaks and low dips at which the optical coefficients are almost quenched, as seen by the example in Fig. 28 for the prototypical AdPh₄.

The optical response is thus strongly dependent on the incident photon energy, with most compounds showing a maximum of the SHG coefficients above 2 eV and a THG maximum just below 2 eV (see e.g., Fig. 29). In general, the white-light emission efficiency is expected to depend on the exciting wavelength.⁶⁴⁸ However, this does not seem to be the case for the adamantane-type cluster molecules.^320,571 This might be related to the fact that in the adamantane-type cluster molecules, white-light emission is achieved by an excitation in a generally non-resonant region of the nonlinear optical spectrum (1.1–1.3 eV), however, where the onset of the optical nonlinearities is already pronounced. As this spectral region is followed by a steep gradient of the nonlinear optical susceptibilities, the white-light emission efficiency might be further increased, provided it correlates (as currently assumed) with the optical nonlinearities.

Fig. 29. Second-harmonic generation (top, χ⁽²⁾_xxx component) and third harmonic generation (bottom, χ⁽³⁾_xxxx component) coefficients (absolute values) calculated as a function of the incident laser wavelength for the isolated [PhSi{CH₂Sn(S)Ph}₃] cluster (blue dots) and the corresponding crystal (orange dots) within the independent particle approximation at the DFT equilibrium geometry. Intensities are scaled by the respective maximum for each structure, and energies are shifted relative to the energy gap.^642,644.

5. Materials properties (crystalline/amorphous, glass formation): comprehension and prediction

A common trend identified in multiple structures with adamantane and adamantane-like cores is the inheritance of both the linear and the nonlinear optical response from the parent molecules to dimers and the crystal structures.^642,644 This is admittedly shown in Fig. 29 for the [PhSi{CH₂Sn(S)Ph}₃] molecule. However, a similar trend has been demonstrated also for many other adamantane-based clusters such as [(PhSi)₄S₆] and [(NpSi)₄S₆].^309,571Fig. 29 shows that all spectral features of the isolated molecules can be found in the optical response of the crystals, although the spectral weights are somewhat redistributed. This similarity offers the possibility to roughly estimate, e.g., the second and third order optical nonlinearity by the knowledge of the corresponding single molecule. This is a great advantage, in particular in theoretical studies, due to the computationally less extensive investigations of the single clusters as compared to molecular crystals.

It has been discussed in many publications that an amorphous structure is a prerequisite for white-light generation.⁶⁵² Although the connection between the habitus of the aggregate and its nonlinear optical answer is not completely understood, atomistic calculations show a clear relation between aggregate symmetry and intensity of the nonlinear optical response. We demonstrate this connection employing the prototypical adamantane-type cluster [AdPh₄] as a model system.

Depending on the environment, the geometry and the symmetry of the cluster undergo slight modifications and so does the nonlinear optical response, quantified, in this example, by the average of all the components of the SHG tensor. [AdPh₄] belongs to the space group P4̄2n. This group lacks centrosymmetry, so that SHG generation is expected. Indeed, the isolated cluster in its calculated equilibrium geometry is characterized by a second-order optical response as shown by the blue line in Fig. 30. In aggregates such as [AdPh₄] crystals, the material can be thought of as a periodic repetition of [AdPh₄] dimers.⁶⁴⁴ The dimers are arranged in a manner that is still not centrosymmetric, however, the deviation from the centrosymmetry is lower than in the case of the isolated clusters. The SHG response per molecule, shown in Fig. 30 (orange line) features all the spectral signatures predicted for the isolated cluster, however, with a lower intensity.

Fig. 30. Second-harmonic generation per cluster (the average of the absolute value of all tensor components is shown) calculated within the independent particle approximation as a function of the incident laser wavelength for the isolated [AdPh₄] cluster with the DFT equilibrium geometry (blue line) and with the geometry of a cluster dimer cut out from a [AdPh₄] crystal (orange line).⁶⁴⁴.

Artificially modifying the structure towards centrosymmetry further lowers the SHG coefficients. The same behavior is observed for other optically nonlinear molecular clusters. Differences in the symmetry of monomer and dimer structures can also greatly influence the magnitude of the optical response, yet maintaining its overall form. Especially the differences of the nonlinear optics of free-standing dimers compared to their crystal counterparts show that the habitus of the material offers a path to tuning the symmetry and thus the nonlinear optical properties. WLG is only observed in samples with amorphous morphology. The crystalline members of the class of adamantane-based cluster compounds show a different nonlinear optical response, generally SHG originating from the bulk (in the case of crystals lacking inversion symmetry) or from surfaces or interfaces and defects (in the case of centrosymmetric crystals).⁶⁴⁹ This is shown in Fig. 31 for the crystalline compound [(PhSi)₄S₆] (568) (a) and for the amorphous material [(PhSn)₄S₆] (587) (b) as examples. Both clusters are provided with the same organic phenyl ligands and differ just by the exchange of Si atoms by Sn atoms in the adamantane shaped cluster cores. The solid with the {SiS} cluster core (568) shows the typical powder diffractogram of a crystal (Fig. 31a). When irradiated by an optical laser line with wavelength 979 nm, it reacts with an intense second-harmonic at 489 nm. In contrast, the X-ray diffractogram obtained from the solid of the corresponding {SnS} cluster (587) yields a pattern typical for a completely disordered material like a glass, not comprising any information about structural long-range order between the molecules (Fig. 31b). However, the optical response to NIR irradiation at 979 nm is now found to be a broad white emission that spans the entire visible portion of the white-light spectrum.

Fig. 31. NLO responses from the clusters 568 (a) and 587 (b) (top). The driving excitation is visible at 979 nm (1.265 eV) in each spectrum. The 2nd-harmonics of (a) is seen at 489.5 nm (2.53 eV), while (b) depicts a broad white spectrum. The respective X-ray patterns are also shown below indicating that 568, the SHG-material, is clearly crystalline while the WLG material 587 shows a typical structure factor S(Q) of an amorphous solid. (c) shows the NLO response of cluster 591 indicating SHG, although the X-ray structure factor clearly designates an amorphous solid (reproduced from ref. 657 with permission from the authors under CC BY 4.0).

Meanwhile, a large number of solids of this type could be synthesized showing this correlation between morphology and optical behavior.⁵⁷¹ While all crystalline materials have been identified as materials for second-harmonic generation (SHG), it however turned out that among the amorphous materials, it is only the vast majority responding by white-light generators (WLG). A few apparently amorphous clusters whose diffractograms resemble those of glasses, with pronounced structural disorder at the molecular level, nevertheless exhibit SHG upon NIR irradiation. The optical response and X-ray diffractogram of one such example, the {SnS} cluster decorated with naphthyl ligands, [(NpSn)₄S₆] (591), are shown in Fig. 31c. Although the X-ray diffractogram of (591) does not show typical Bragg peaks but rather resembles the typical structure factor S(Q) for a glass, the optical response when irradiated with the NIR line at 979 nm is found to be SHG.

In trying to understand this behavior, two questions come to mind: What controls the solidification of these cluster molecules into either an amorphous or a crystalline state, and why is pronounced microscopic disorder a prerequisite for a nonlinear response in the form of WLG? In order to answer these questions, it is compulsory to first obtain precise knowledge of the interactions between the clusters, which however requires detailed knowledge of their electronic structure as a function of composition. Then, it must be further understood how the molecular and electronic structure is altered when the clusters aggregate into either a crystalline or amorphous condensed phase. This is a prerequisite for finding approaches from the observed differences that may lead to an understanding of the different optical behavior of these clusters in the two different solid-state morphologies. For this purpose, several optical studies were performed on different cluster systems.⁶⁵³ Furthermore, the electronic structures of many clusters from this group with different organic ligands and {QE} cluster cores were calculated, as well as interaction energies between the clusters for simple arrangements of two to four clusters as simple models to distinguish between different contributions to the interactions.^309,644 Also, experimental investigations were accomplished to explore the mutual orientation of the clusters in the amorphous solid.^654–657 It showed up thereby however, that the control of the morphology is complex and an assignment amorphous/WLG, crystalline/SHG is oversimplified. It was however found from EXAFS experiments⁶⁵⁸ that the molecular structure of adamantane-like cluster materials showing SHG (586 and 591) was close to that found from quantum chemical calculations,⁶⁵⁹ while those showing WLG (587 and 602) considerably deviated from these structures.

More detailed studies carried out on the WLG compound 587 and the SHG compound 591 using X-ray diffraction combined with molecular Reverse Monte Carlo (m-RMC) simulations further revealed that this observation results from significantly distorted cluster cores in the compounds showing WLG. The distortions originate from sulfur atoms moving out of their equilibrium positions, towards other sulfur atoms of neighboring molecules. This may result from strong interactions between the cores of the individual clusters, as was also suggested by quantum chemical calculations,^309,660 where smaller cluster aggregates of two to four molecules were assumed as simple models for a disordered phase. Indeed, the mutual cluster orientations predicted there for the WLG compound 587 were also found in the experimental X-ray/RMC-studies⁶⁵⁷ supporting the theoretical findings. Similar experimental studies on the SHG compound 591 revealed no evidence for distorted cluster cores. The mutual molecular orientation of the clusters in the solid state also suggested stronger intermolecular interactions via the organic ligands, which also supports the quantum chemical calculations made earlier. In addition, electron microscopy could reveal sections of nanocrystallinity, which may additionally explain the findings by ordered parts of the material.

The observation of additional cluster core distortions in the material exhibiting strong WLG compound 587, further highlights the point made earlier that a clear relationship exists between structural and molecular symmetry and intensity of the nonlinear optical response.

6. Conclusion and outlook

The number of compounds based on adamantane-type core architechture is vast, and the elemental compositions of the cluster cores as well as the variety of the substituents is extremely diverse. While this naturally leads to different chemical reactivities and unique electronic structures, a number of them share luminescence phenomena. Only recently, strong second-harmonic generation as well as more uncommon nonlinear optical properties in the form of directed white-light emission have been observed, which seem to be a consequence of the unique adamantane type architecture – with its relatively dense electronic structure and its inherently missing inversion symmetry – as well as of the compounds' arrangement within the solid material.⁵⁷¹ Assuming that these phenomena could in theory be observable for other adamantane-type cluster compounds, we have summarized all classes of inorganic and a selection of organic admantanes in this survey. Most of these compounds have not been fully investigated for their physical properties so far, but we suggest that doing so could be a great chance to gain understanding on the optical phenomena in this class of compounds and its potential use. The plethora of different compositions and structural peculiarities is an excellent basis for future investigations into this field, which could become a library of compounds that fulfils any desired properties in regards of wavelength, bandwidth, intensity, and directionality in combination of convenient synthetic access, robustness, and processability of the material.

Abbreviations

IDipp

1,3-Bis(2,6-diisopropylphenyl)imidazole-2-ylidene

HMDS

1,1,1,3,3,3-Hexamethyldisilazide

TACNMe

1,4,7-Trimethyl-1,4,7-triazacyclononane

Bn

Benzyl

Cp*

Pentamethylcyclopentadienyl

DMAP

Dimethylamine borane

BAr^F

[B[3,5-(CF₃)₂C₆H₃]

ⁿ Bu

Normal butyl

^t Bu

Tertiary butyl

Diglyme

Bis(2-methoxyethyl) ether

DMPyr

1,1-Dimethylpyrrolidinium

OTf

O₃SCF₃

cod

1,5-Cyclooctadiene

OAc

Acetate

acac

Acetylacetonate

BMIm

1-Butyl-3-methyl-imidazolium

NTf₂

Bistrifluoridomethansulfonimide

TMEDA

Tetramethylethylenediamine

ⁱPr

Isopropyl

DME

1,2-Dimethoxyethane

Ar^Me6

C₆H₃-2,6(C₆H₂-2,4,6-Me₃)₂

mes

2,4,6-Me₃-C₆H₂

Tp^Me2

Tri(3,5 dimethylpyrazolyl)borate)

TACN

1,4,7-Triazacyclononane

DMSO

Dimethyl sulfoxide

Cp^xPh

C₅Me₄Ph

OHF

1,2,3,4,5,6,7,8-Octahydrofluorenyl

dmae

N,N-Dimethylaminoethanolate

TFA

Trifluoacetic acid

H₄cit

Citric acid

H₂DBcat

3,5-Di-tert-butylcatechol

HBO

2-(2′-Hydroxyphenyl)benzoxazole

tach

1,3,5-Triaminocyclohexane

en

Ethylendiamine

H₅hpdta

Hydroxypropanediaminotetraacetic acid

HIPAP

N-(tert-Butyl)-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)-propanamide

tdmap

OC(CH₂NMe₂)₃

S-Phoz

2-(4′,4′-Dimethyloxazoline-2′-yl)thiophenolate

bpea

N,N-Bis(2-pyridylmethyl)ethylamine

[3,5-(CF₃)₂C₆H₃]₄B]⁻

dien

Diethylenetriamine

Medien

N′-Methyldiethylenetriamine

R-ida

N-(R)Iminodiacetate

^C Pe

Cyclopentane

tame

tert-Amyl methyl ether

Htphpn

N,N,N′,N′-Tetra-(2-methylpyridyl)-2-hydroxypropanediamine

pz

Pyrazolyl

H₂BMAP

2-[bis(2-mercaptoethyl)aminomethyl]pyridine

Py

Pyridine

H₅HMeXCG

N,N′-(2-Hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine)

H₅HPhXCG

N,N′-(2-Hydroxy-5-phenyl-1,3-xylylene)bis(N-(carboxymethyl)glycine)

Dma

N,N-Dimethylacetamid

Hbpbp

2,6-Bis((N,N′-bis-(2-picolyl)amino)methyl)-4-tert-butylphenol

{(TACN)CH₂}₂CHOH

1,3-Bis(1,4,7-triaza-1-cyclononyl)-2-hydroxypropane

N-Et-HPTB

N,N,N′,N′-Tetrakis(2-(1-ethylbenzimidazolyl))-2-hydroxy-1,3-diaminopropane

dppoe

1,2-Bis(diphenylphosphine oxide)ethane

dppe

1,2-Bis(diphenylphosphino)ethane

H₃HMPM

2,6-Bis[{{(1-hydroxy-2-methylpropan-2-yl)(pyridine-2-ylmethyl)}amino}methyl]-4-methylphenol

Me₂phen

2,9-Dimethyl-1,10-phenanthroline

BIK

Bis(2-methyl-imidazole-2-yl)ketone

^t Bu₂DED

1,1-Dicarbo-tert-butoxy-2,2-ethylenedithiolate

tpdt

3,4-Thiophenedithiolate

α-tpdt

2,3-Thiophenedithiolate

H₄pymtH

3,4,5,6-Tetrahydropyrimidine-2-thione

H₃O3N4

1-Me-4-OH-3,4-bis(CH₂N(CH₂C₅H₄N)(CMe₂CH₂OH)–C₆H₂

Fc

Ferrocenyl

2-TBI

2-Thiobenzimidadzol

Mbis

1,1′-Methylenebis(3-methylimidazoline-2-selone)

DAMS

Trans-4-(4-dimethylamino-styryl)-N-methyl-pyridinium

bipy

Bipyridine

ⁿ Pr

Normal propyl

^secBu

Secondary butyl

phen

1,10-Phenanthroline

^o Py

ortho-Pyridyl

Tab

4-(Trimethylammonio)benzenethiolate

[2.2.2]-crypt

4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane

POPYH₄

N,N′-Bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide

dap

1,2-Diaminopropane

tepa

Tetraethylenepentamine

Vio

Viologen dication

TMPyP

5,10,15,20-Tetrakis(N-methyl-4-pyridyl)porphyrin

DMBPE

N,N′-Dimethyl-1,2-bis(4-pyridinium)-ethylene

Cyclam

1,4,8,11-Tetraazacyclotetradecane

Trien

Triethylentetramin

Teta

Triethylenetetramine

Thex

1,1,2-Trimethylpropyl

Np

Naphthyl

Sty

para-Styryl

Cy

Cyclohexyl

Cp

Cyclopentadienyl

Dipp

2,6-Diisopropylphenyl

DMEGqu

N-(1,3-Dimethylimidazolidin2-ylidene)quinoline-8-amine

8-HQ

8-Hydroxyquinoline

H₂naphpz

2-[1H-Pyrazol-5(3)-yl]naphthalene-1-ol

dpan

6-Diphenylphosphinoacenaphth-5-yl

L_OEt

[Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]⁻

3-NO₂Tp

3-Nitrotrispyrazolylborate

SON

(Benzothiazole-2-yl)phenolate

HBT

2-(2-Hydroxyphenyl)benzothiazole

H₃L

2-Hydroxy-N-[2-hydroxy-3-[(2hydroxybenzoyl)amino]propyl]benzamide

C₄mim

1-Butyl-3-methylimidazolium

da6aH₆

p-Methyl-dimethyldiazacalix[6]areneH₆

HMTA

Hexamethylentetramine

HBDA

Hexakis(trimethylsilyl)benzdiamidine

cpz

2-Chloro-10-(3-dimethylaminopropyl(phenothiazine)

DENC

N,N-Diethylnicotinamide

Pz^iPr2H

3,5-Diisopropylpyrazole

DASO

Diallyl sulfoxide

Amt

1,3-Diamino-1,2,2-trimethylcyclopentane

CgP

1,3,5,7-Tetramethyl-2,4,6-trioxa-8-phosphatricyclo[3.3.1.1]-decane

nmp

N-Methyl-2-pyrrolidinone

teed

N,N,N′,N′-Tetraethylethylenediamine

BPBACy

Bis(1-propylbenzimidazol-2-yl)-trans-1,2-cyclohexane

dpipa

N,N′-Dimethylpiperazine

PoxIm

N-Phenyl-N′-{bis(tertbutyl)phosphinoxide}-imidazolylidene

Dabco

1,4-Diazabicyclo[2.2.2]octane

tib

1,3,5-Tris(1-imidazolyl)benzene

pyr

Pyrrolidine

dppbO₂

1,2-bis(diephenlyphospineoxide) benzol

tdpmO₃

tris(diephenlyphospineoxide) methan

BPPIP

Bis-triphenylphosphonio-isophosphindolide

THP

Tetrahydropyran

tren

Tris(2-ethylamino)amine

gua

Guanidine

bme*daco

Bis(N,N′-2-mercapto-2-methylpropyl)1,5-diazocyclooctane

Bdpman

N,N′-Bis(diphenylmethyl)-3,7-diazabicyclo[3.3.1]nonane

Hbdmap

1,3-Bis-(dimethylamino)-propan-2-ol

ⁿ Hep

Normal heptane

TAEA

Tris(2-aminoethyl)amine

tdci

1,3,5-Trideoxy-1,2,5-tris(dimethylamino)-cis-inositol

Hchp

6-Chloro-2-hydroxypyridine

dmit

4,5-Dimercapto-1,3-dithiole-2-thionato

EDTA

Ethylenediamine-tetraacetate

BMMIm

1-Butyl-2,3-dimethyl-imidazolium

MCPBA

m-Chloroperbenzoic acid

Author contributions

All athors agreed on the concept of the article and co-wrote the paper.

Conflicts of interest

There are no conflicts to declare.