Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2022 Dec 7;61(50):20308–20315. doi: 10.1021/acs.inorgchem.2c02717

Gold(I)···Lanthanide(III) Bonds in Discrete Heterobimetallic Compounds: A Combined Computational and Topological Study

Daniel Blasco †,‡,*, Dage Sundholm †,*
PMCID: PMC9768751  PMID: 36475614

Abstract

graphic file with name ic2c02717_0006.jpg

The chemical nature of the ligand-unsupported gold(I)–lanthanide(III) bond in the proposed [LnIII(η5-Cp)2][AuIPh2] (Ln–Au; LnIII = LaIII, EuIII, or LuIII; Cp = cyclopentadienide; Ph = phenyl) models is examined from a theoretical viewpoint. The covalent bond-like Au–Ln distances (Au–La, 2.95 Å; Au–Eu, 2.85 Å; Au–Lu, 2.78 Å) result from a strong interaction between the oppositely charged fragments (ΔEintMP2 > 600 kJ mol–1), including the aforementioned metal–metal bond and additional LnIII–Cipso and C–H···π interactions. The Au–Ln bond has been characterized as a chemical bond rather than a strong metallophilic interaction with the aid of energy decomposition analysis, interaction region indicator, and quantum theory of atoms in molecules topological tools. The chemical nature of the Au–Ln bond cannot be fully ascribed to a covalent or an ionic model; an intermediate situation or a charge shift bond is proposed. The [AuIPh2]− anion has also been identified as a suitable lanthanide(III) emission sensitizer for La–Au and Lu–Au.

Short abstract

The nature of the predicted chemical bond between gold(I) and lanthanide(III) and the role of gold(I) fragments as lanthanide(III) emission sensitizers are investigated.

1. Introduction

The reactivity of the extremely stable dicyanoaurate(I) anion {[AuI(CN)2]−} toward f-block metal(III) salts has recently been a subject of sporadic research that mainly has focused on the efficient sensitization of the monochromatic line-like emission of the lanthanide(III) cations.1−12 Other relevant properties such as single-molecule magnetism (SMM)10 and birefringence have been examined.5 It is accepted, even as textbook knowledge,13 that lanthanide-based emission is a result of parity-forbidden radiative 4f–4f transitions [or parity-allowed 4f–5d transitions in the case of, e.g., cerium(III)] because of an energy transfer (ET) from the lowest excited triplet state of the (metallo)ligand, the so-called sensitizer, to the lanthanide atom.14 Hence, the global emission efficiency strongly depends on the electronic structure of the sensitizer and the lanthanide, which requires an appropriate energy match for allowing the whole cascade of intersystem crossings (ISCs) and ETs to occur. Several studies have demonstrated that gold(I) and silver(I) dicyanometallates {[MI(CN)2]−; MI = AuI or AgI} and platinum(II) tetracyanometallates {[PtII(CN)4]2–} are among the most efficient sensitizers because of not only the similarity between their energy levels and those of the lanthanide(III) acceptors but also spin–orbit coupling (SOC) effects. More precisely, the metal···metal-based low-lying triplet states of the aurophilic AuI···AuI or metallophilic MI(d10)···MII(d8) (MI = AuI or AgI; MII = PtII or PdII) interactions that are found within LnIII[AuI(CN)2]3·3H2O [LnIII = LaIII, PrIII, NdIII, CeIII, SmIII, EuIII, GdIII, TbIII, or DyIII (Scheme 1, top left)]7−9,15 and terbium(III) or europium(III) heterotrimetallic solid state solutions,2,11 respectively, have been identified as the best ET donor states. Aurophilic attraction is an extremely important and recurrent structural motif in the chemistry of gold(I)16−18 that has been studied theoretically in detail.19 It is characterized by unexpectedly short gold(I)···gold(I) distances and high interaction energies of 30–50 kJ mol–1. It is relevant not only from a structural point of view but also because it stabilizes reactive intermediates of catalysis.20 Its occurrence between gold atoms in higher oxidation states (AuIII) is still controversial.21 The proposals of all of the articles reviewed for the elaboration of this work are based on qualitative interpretations of the luminescence spectra, lifetimes, and quantum yields without any further theoretical support.

Scheme 1. Representative Examples of Heterometallic Gold(I)–Lanthanide(III) Complexes and Theoretical Models.

Scheme 1

Open in a new tab

LnIII[AuI(CN)2]3·3H2O (top left, water molecules omitted for the sake of clarity), [Au2–ILnIII]+ model (bottom left), [LnIIIAuI(dpfam)3]OTf {dpfam = N,N′-bis[(2-diphenylphosphino)phenyl]formamidinate; (OTf)− = (CF3SO3)− (bottom center)}, and the presently studied [LnIII(η5-Cp)2][AuIPh2] (Ln–Au; Cp = cyclopentadienide; Ph = phenyl; right) models.

Very little is known about a possible direct interaction between gold(I) and lanthanide(III) atoms. In a report by Páez-Hernández et al., they studied the intermetallic bond in the C2v-shaped [Au2–ILnIII]+ (LnIII = EuIII or LuIII) and [Au2–IYbII] species (Scheme 1, bottom left) through density functional theory (DFT), complete-active-space self-consistent-field (CASSCF), and second-order complete-active-space perturbation theory (CASPT2) calculations.22 They concluded that these Au–I–LnIII bonds have a large two-center, two-electron (2c-2e) covalent contribution arising from the Au(6s)–Ln(5d6s) hybridization. Despite being good models for intermetallic compounds,23,24 they are poorly descriptive for the purposes of coordination chemistry, where ancillary ligands, especially when dealing with lanthanide cations, play a pivotal role. A recent paper by Roesky et al. illustrated the first example of heterometallic molecular gold(I)–lanthanide(III) complexes without mediation of cyanide ligands.25 The authors cleverly employed the tetradentate ligand dpfam {dpfam = N,N′-bis[(2-diphenylphosphino)phenyl]formamidinate}, featuring “hard” (nitrogen) and “soft” (phosphorus) donor sites, for a stepwise and selective coordination of lanthanum(III)/neodimium(III) and gold(I) (Scheme 1, bottom center). The intermetallic distances determined by X-ray diffraction are in the limit for the van der Waals interaction (LaIII···AuI, 4.24 Å; NdIII···AuI, 4.20 Å). However, they proposed a possible metal···metal interaction in the first excited state.

To date, an experimental proof of ground state gold(I)–lanthanide(III) bonds and/or interactions is lacking, which is even more striking when considering the plethora of structurally authenticated combinations of other main- and d-block metals with lanthanides and even with actinides.26 In a particularly impressive example, a naked lanthanide(III) atom is stabilized by only metal···metal bonds with three rhenocene {[ReI(η5-Cp)2]−} anions.27 The aforementioned lack of knowledge is probably due to the choice of the coordinating dicyanoaurate(I) anion in almost all studies dealing with this subject. To address it and also to unveil the possible derived optical consequences, we herein present a computational and topological study of three models featuring an unsupported interaction between the noncoordinating diphenylaurate(I) anion ([AuIPh2]−) and bis(η5-cyclopentadienide)lanthanide(III) cations {[LnIII(η5-Cp)2]+; LnIII = LaIII, EuIII, or LuIII} henceforth designated, for the sake of brevity, as Ln–Au (Scheme 1, right). With regard to the choice of the [LnIII(η5-Cp)2]+ component, closed-shell lanthanum(III) ([Xe]) and lutetium(III) ([Xe] 4f14) are adopted to favor possible metallophilic interactions, whereas europium(III) ([Xe] 4f6) was considered a suitable representative of open-shell lanthanide cations. Cyclopentadienide ancillary ligands are ideal as each one saturates three coordination vacancies of the highly electron-demanding lanthanide(III) cation while being addressed as spectator ligands.

2. Computational Details

All calculations were carried out using TURBOMOLE version 7.5.1.28,29 The optimized molecular structures and orbitals were visualized and rendered using the latest version of UCSF ChimeraX.30Ln–Au models were built from scratch and optimized without any symmetry constraints at the DFT level using the PBE0 functional31−33 and the def2-TZVP basis sets.34,35 Dispersion interactions were considered with the semiempirical D3(BJ) correction.36,37 The resolution-of-the-identity (RI) approximation38−41 was used to accelerate the calculations. Effective core potentials (def2-ECP) were used for gold and the lanthanides [Au, 60 core electrons (CE); La, 46 CE; Eu, 28 CE; Lu, 28 CE].42 All structures were verified as true local minima by computing the vibrational frequencies.43

The gold(I)–lanthanide(III) interaction energies (ΔEint in eq 1) were calculated at the restricted Hartree–Fock (RHF/def2-TZVP)44 and second-order Møller–Plesset perturbation theory (MP2/def2-TZVP)45−47 levels using eq 1 for the counterpoise correction to the basis set superposition error (BSSE).48,49

2. 1

where EAB(AB), EA, and EB(AB) are the energies of the complex and the fragments calculated using the basis sets of the complex.

According to energy decomposition analysis (EDA),50 the instantaneous interaction energy between two fragments (ΔEint in eq 2) can be partitioned into the sum of quasiclassical electrostatic Inline graphic, exchange–repulsion Inline graphic, orbital relaxation Inline graphic, correlation Inline graphic, and dispersion Inline graphic contributions:

2. 2

Whereas the physical meaning of the ΔEele, ΔEcorr, and ΔEdisp contributions is self-explanatory, ΔEex–rep (or Pauli repulsion, ΔEPauli) accounts for the destabilizing interaction between electrons of the same spin and ΔEorb stands for orbital relaxation and mixing between fragments. The present formulation of EDA is implemented in TURBOMOLE only at the RHF and DFT levels of theory.

The quantum theory of atoms in molecules (QTAIM)51,52 electron-density descriptors ρe(r), Inline graphic, and H, and the recently proposed interaction region indicator (IRI, eq 3),53 have been computed with the latest version of Multiwfn.54 The IRI isosurfaces

2. 3

have been plotted with VMD.55

The optimized molecular structures of the ground state were used in time-dependent DFT (TD-DFT)56−60 calculations of the first vertical singlet (S1 ← S0) and triplet (T1 ← S0) excitation energies using the PBE0 functional31−33 and the def2-TZVP basis sets.34,35

3. Results and Discussion

3.1. Structure Optimization

The molecular structure of the Ln–Au models optimized at the PBE0/D3(BJ)/def2-TZVP level is shown in Figure 1. A selection of bond lengths and bond angles are listed in Table 1. We obtained remarkably short AuI···LnIII distances in contrast to recurrent measurements of nonbonding distances between the metals, which may be a consequence of the choice of the ancillary ligands attached to gold(I) (phenyl vs cyanide) and lanthanide(III) (cyclopentadienide vs aquo, nitrate, and/or polypyridines). The overall stability of the rigid framework, which is driven by, e.g., the intermetallic μ2-cyanido coordination, probably overrules the stability of single AuI···LnIII bonds and/or interactions.

Figure 1.

Figure 1

Open in a new tab

Molecular structures of the Ln–Au models. Color code: C, gray; H, white; Au, yellow; Eu, aquamarine blue; La, sky blue; Lu, green.

Table 1. Selected Bond Lengths (in angstroms) and Angles (in degrees) of the Ln–Au Models, with RAu–Ln Distances (in angstroms) According to the Additive Covalent Radius Conventiona,b.

  AuI···LnIII AuI–Cipso LnIII–Cipso LnIII–Cmeta Cipso–AuI–Cipso
La–Au 2.95 (3.04),a (3.43)b 2.06 3.28 – 159
Eu–Au 2.85 (2.92),a (3.34)b 2.04, 2.09 2.83, 3.90 2.84 172
Lu–Au 2.78 (2.86),a (3.23)b 2.05, 2.11 2.69, 4.01 2.75 176
Open in a new tab
a

Data from refs (61) and (62).

b

Data from ref (63).

When the computed AuI···LnIII distances are compared to the sum of the single-bond covalent radii (eq 4) of the involved atoms

3.1. 4

one obtains a coarse idea of the covalent character of the Au–Ln bond. Table 1 also includes RAu–Ln values calculated from the data sets of covalent radii of Pyykkö et al.61,62 and Cordero et al.63 The decreasing trend in the AuI···LnIII distances with an increase in the atomic number of LnIII [d(Au–La) > d(Au–Eu) > d(Au–Lu)] agrees with the lanthanide contraction effect.13 The computed AuI···LnIII distances are roughly 0.1 Å shorter than the Au–Ln estimates. Thus, a single covalent bond is more likely than a metallophilic interaction between the gold(I) and lanthanide(III) atoms. The Wiberg bond indices (WBIs) of the Au–Ln bond and other WBIs of interest are listed in Table 2. The WBI values are >0.6, suggesting that there is a covalent bond between the metals. The WBI of the Au–Ln bond of the Ln–Au models can be compared to those reported by Roesky et al. for the [LaIIIAuI(dpfam)3]+ cation.25 Their WBI values calculated at different DFT levels of theory range between 0.12 [BP/D3(BJ)/def2-SVP] and <0.02 [PBE0/D3(BJ)/def2-TZVP*]. These values are small in comparison to the WBI value of the Ln–Au models.

Table 2. Selected WBIs (PBE0/D3(BJ)/def2-TZVP level of theory) of the Ln–Au Models.

  AuI···LnIII AuI–Cipso LnIII–Cipso LnIII–Cmeta
La–Au 0.62 0.67, 0.67 <0.10 –
Eu–Au 0.63 0.48, 0.75 0.19 0.19
Lu–Au 0.68 0.43, 0.72 0.19 0.18
Open in a new tab

The effective charges of the gold(I) and lanthanide(III) atoms in the Ln–Au models have been calculated using the natural population analysis (NPA) approach. The charges are compared in Table 3 to those of the corresponding isolated [LnIII(η5-Cp)2]+ (model Ln) and [AuIPh2]− (model Au) ions optimized at the same level of theory [PBE0/D3(BJ)/def2-TZVP]. In the isolated ions as well as in the Ln–Au models, the metals have an effective charge that is much smaller than their formal oxidation state. In the formation of the Au–Ln bond, electron density is transferred from gold(I) to lanthanide(III). The NPA charge of gold(I) increases by ∼0.2. The positive charge of the lanthanide(III) atom in Eu–Au and Lu–Au decreases more than it increases in gold(I), suggesting a further stabilizing role of the LnIII–Cipso bonds.

Table 3. NPA Charges (PBE0/D3(BJ)/def2-TZVP level of theory) of the Ln, Au, and Ln–Au Models.

  LnIII AuI Δ(LnIII)a Δ(AuI)a
La 1.93 – – –
Eu 1.77 – – –
Lu 2.03 – – –
Au – 0.30 – –
La–Au 1.75 0.48 –0.18 +0.18
Eu–Au 1.33 0.49 –0.45 +0.18
Lu–Au 1.52 0.49 –0.57 +0.19
Open in a new tab
a

Δ(LnIII)(Δ(AuI)) = Ln–Au – Ln (Au).

A short metal···metal distance, even if it is not supported by ancillary ligands (as in the present case), is not enough to guarantee that there is a covalent bond. Pyykkö et al. clearly stated that one cannot estimate bond lengths and bonding character for strongly ionic systems by adding the covalent radii.61,62 There are some concerns about the pure covalent character of the Au–Ln bond. We note that the f-block ions are “noble gas-like” regarding covalent bonding due to the efficient shielding of the 4f valence orbitals by the outer electron shells.13 Because gold is the most electronegative metal of the periodic table (χP = 2.54),64 the combination of the [AuIPh2]− anion with highly charged lanthanide(III) cations leads to a significant Coulombic attraction. We therefore carried out an energy decomposition analysis of the Au–Ln bond to elucidate its bonding character (vide infra).

There is an evident shift of the [LnIII(η5-Cp)2]+ cation with respect to the [AuIPh2]− anion from an almost eclipsed conformation in La–Au toward formation of a AuI–Cipso bond in Eu–Au and Lu–Au. Depletion of the electron density of Cipso is reflected in a weakening of the AuI–Cipso bond, which is suggested by its elongation (Table 1) and the decreasing WBI (Table 2). The presence of the [LnIII(η5-Cp)2]+ fragment leads to a significant distortion of the ideal linear environment of the dicoordinated [AuIPh2]− anion (Figure 1 and Table 1). In the extreme case, both AuI–Cipso bonds would be bent toward the lanthanum(III) atom, suggesting that lanthanide(III) completes its coordination sphere by withdrawing electron density from the AuI–Cipso bond or even from Cmeta in Eu–Au and Lu–Au. This will be further assessed with the aid of topological tools (vide infra).

3.2. Energy Decomposition Analysis (EDA)

The counterpoise-corrected interaction energies between the gold(I) and lanthanide(III) fragments calculated at the RHF and MP2 levels are listed in Table 4. We considered the experimentally plausible heterolytic fragmentation into [AuIPh2]− and [LnIII(η5-Cp)2]+ ions instead of the homolytic dissociation into [AuIPh2]• and [LnIII(η5-Cp)2]• radicals.

Table 4. Counterpoise-Corrected Interaction Energies of Ln–Au (in kilojoules per mole) Calculated at the RHF/def2-TZVP and MP2/def2-TZVP Levels.

  ΔEintRHF ΔEintMP2 ΔEintMP2 – ΔEintRHF (%)a
La–Au –467.69 –602.99 –135.30 (22.44)
Eu–Au –456.71 –604.93 –148.23 (24.50)
Lu–Au –468.49 –630.17 –161.68 (25.66)
Open in a new tab
a

Percentages are calculated with respect to ΔEintMP2.

The interaction energies calculated at the MP2 level are >600 kJ mol–1 and are similar for the three molecules. The large interaction energies suggest that there is a bond between the metals and that the short Au–Ln distance is not due to metallophilic interactions between closed-shell gold(I) and lanthanide(III). The binding energy can be compared to typical aurophilic interaction energies of 30–50 kJ mol–1, which is of the same the size as the binding energy of strong hydrogen bonds. Aurophilicity is even the strongest metallophilic interaction.16−18 The bond between the fragments cannot be assigned to a single interaction. The role of C–H···π interactions cannot be ignored (vide infra). The difference between the interaction energies calculated at the RHF Inline graphic and MP2 Inline graphic levels is the electron correlation contribution to the stabilization of the Au–Ln bond. Electron correlation accounts for >20% of the binding energy at the MP2 level. Because a previous study showed that the wave function of complexes with TM–Ln (TM = transition metal) bonds does not have a significant multiconfiguration character,65 we assume that the energy difference can be ascribed to the dispersion interaction between [AuIPh2]− and [LnIII(η5-Cp)2]+ and dynamical correlation effects on the Au–Ln bond.

EDA splits interaction energies Inline graphic into contributions from electrostatic interaction Inline graphic, Pauli repulsion Inline graphic, and orbital relaxation Inline graphic. EDA of the interaction energy between [AuIPh2]− and [LnIII(η5-Cp)2]+ was calculated at the PBE0 level (Table 5). The EDA contributions belong to the chemical bonding vocabulary of today and introduce an analogy with the heuristic ionic and covalent models used among synthetic chemists.66 We discuss trends among the Ln–Au models rather than providing an absolute EDA partitioning, because there is no obvious relation between the EDA values and periodic trends among the lanthanide ions, which is in contrast to the geometrical parameters listed in Table 1. The electrostatic component is ∼60% of the interaction energy, whereas the orbital relaxation contribution is <30%. We cannot assign the Au–Ln bonds as pure covalent or ionic bonds, which has also been pointed out in previous studies of TM–Ln systems.27,65,67,68 The covalent orbital contribution to the bond is significant. However, the contribution from Pauli repulsion is larger with an opposite sign. An appropriate description seems to be that an ionic-reinforced weak covalent bond keeps the fragments together. One should though realize that this an oversimplification of the predicted and presumably also of the experimental bonding character.

Table 5. Energy Decomposition Analysis (EDA in kilojoules per mole) of the Ln–Au Models Calculated at the PBE0/D3(BJ)/def2-TZVP Level of Theory.

  ΔEint ΔEele (%)a ΔEex–rep ΔEorb (%)a ΔEcorr (%)a ΔEdisp (%)a
La–Au –580.42 –468.30 (55.50) 263.31 –240.06 (28.45) –84.57 (10.02) –50.79 (6.02)
Eu–Au –574.50 –525.99 (58.23) 328.87 –249.68 (27.64) –80.99 (8.97) –46.71 (5.17)
Lu–Au –598.53 –550.05 (57.02) 366.08 –276.41 (28.66) –91.37 (9.47) –46.78 (4.85)
Open in a new tab
a

The percentages are calculated with respect to the sum of the stabilizing contributions, i.e., ΔEele + ΔEorb + ΔEcorr + ΔEdisp.

3.3. Interaction Region Indicator Topological Analysis

The interaction region indicator (IRI) method53 is a recently proposed real-space function based on the reduced density gradient (RDG) aiming to visualize covalent and noncovalent interactions. The IRI developers claim that it solves certain flaws of the well-established density overlap regions indicator (DORI).69 Because the DORI and IRI isosurfaces are weighted by the sign of the second largest eigenvalue of the Hessian of the electron density [sign(λ2)·ρe(r)], one can visually distinguish attractive [blue to green, sign(λ2)·ρe(r) < 0], van der Waals [green, sign(λ2)·ρe(r) ≈ 0], and repulsive [green to red, sign(λ2)·ρe(r) > 0] interactions. Thus, IRI is well suited for elucidating the van der Waals or covalent/ionic nature of the Au–Ln bond.

The sign(λ2)·ρe(r)-mapped IRI isosurfaces of the Ln–Au models are shown in Figure 2, whereas Figure 3 depicts the raw IRI functions in the plane containing the Cipso–AuI–Cipso moiety and the lanthanide(III) atom. The blueish spot in the slab between the metals in Figure 2 corresponds to an electron-rich area Inline graphic with attractive bonding (λ2 < 0). Its position coincides with the intermetallic axis, suggesting that it is chemical bond rather than a van der Waals (metallophilic) interaction. The LnIII–Cipso and LnIII–Cmeta bonds are also seen in Figure 2, but a clearer view of them is shown in Figure 3. IRI values close to zero are colored black and indicate a strong interaction, although one cannot discern whether it is attractive or repulsive. The green slabs in Figure 2 show C–H···π interactions between the cyclopentadienide ligands of the lanthanide(III) moiety and the phenyl ligands of the gold(I) moiety as well as the π-stacking interactions between the two cyclopentadienide groups.

Figure 2.

Figure 2

Open in a new tab

IRI isosurfaces (isovalue = 1.1) considered with Inline graphic of the La–Au (left), Eu–Au (center), and Lu–Au (right) models. Color code of the atoms: C, gray; H, white; Au, yellow; Ln, cyan. Color code of the IRI isosurfaces: blue, attraction of covalent, hydrogen, halogen, etc., bonds; green, van der Waals interaction; red, repulsion such as steric effects, etc.

Figure 3.

Figure 3

Open in a new tab

IRI plots of the La–Au (left), Eu–Au (center), and Lu–Au (right) models. Brown lines indicate bonds. Red contours correspond to an isovalue of 1.1. Distances are given in angstroms.

The electron density Inline graphic, its Laplacian Inline graphic, and the energy density (H) in the bond critical point (BCP) between gold(I) and lanthanide(III) were computed using the QTAIM approach.51 The BCP descriptors can be related to the bond type and its strength.52 The QTAIM calculations show that there is a BCP along the Au–Ln bond where the gradient norm of the electron density is zero Inline graphic and two eigenvalues of the Hessian of the electron density are negative. Large ρe(r) values (>0.2 au), a negative Inline graphic indicating accumulated electron density, and a negative H represent covalent bonds, whereas small ρe(r) values (<0.1 au), a positive Inline graphic indicating reduced electron density, and a positive H indicate that the bond is ionic.70−72 The Inline graphic and H values listed in Table 6 have opposite signs, suggesting an intermediate between an ionic and a covalent bond, which agrees with previous results. Thus, according to the QTAIM calculations, the Au–Ln bond is neither ionic nor covalent.

Table 6. QTAIM Properties (in atomic units), i.e., Electron Density Inline graphic, Its Laplacian Inline graphic, and Energy Density (H), in the BCP of the Au–Ln Bond of the Ln–Au Models.

  ρe(r) × 10 ∇2[ρe(r)] H × 102
La–Au 0.247 0.066 –0.190
Eu–Au 0.258 0.070 –0.214
Lu–Au 0.266 0.072 –0.232
Open in a new tab

3.4. Optical Properties

The electron transfer from the sensitizer to the lanthanide ion is necessary to activate the 4f–4f radiative de-excitation channel of the latter, which is otherwise a forbidden transition due to the Laporte selection rule.13,14,73 Even though the energy match between the sensitizer and the lanthanide is the most important factor affecting the quantum yield, the sensitizer–lanthanide distance, spectral overlap, etc., play an important role in the luminescence intensity. In the experimental study by Latva et al., they concluded that the quantum yield is largest when the energy is transferred from the lowest triplet state of the sensitizer to the lowest excited state of lanthanide(III).74 The excitation energies of the first excited singlet and triplet states of the Ln–Au models were therefore studied at the TD-DFT/PBE0/def2-TZVP level of theory. The discussion is limited to TD-DFT calculations on the La–Au and Lu–Au models because for the Eu–Au model the TD-DFT calculations yielded physically meaningless results, suggesting that TD-DFT/PBE0 calculations are not well-suited for studies of excited states of the Eu–Au model.

The first singlet-to-singlet and singlet-to-triplet vertical excitation energies of the La–Au and Lu–Au models are listed in Table 7. The molecular orbitals with the largest contribution to these excitations are depicted in Figure 4. The excitation character of the singlet excitation of La–Au is completely dominated (97.2%) by the HOMO (91a) to LUMO (92a) transition corresponding to a mixture of intraligand transfers and a charge transfer from [AuIPh2]− and Cp– (metallo)ligands to the Au–La bonding region. The contribution of 35% to the excitation character is also the dominant contribution to triplet excitation. The significant population of the LUMO orbital in the lowest singlet and triplet states suggests that there is an effective sensitization of the lanthanum(III) ion. The two main contributions to the singlet state of the Lu–Au models are HOMO–1 (106a) to LUMO (108a) and HOMO (107a) to LUMO (108a) with similar weights. The spatial location of the LUMO orbital between the metals is analogous to that of La–Au. However, a large number of orbital excitations that are not listed in Table 7 contribute to the T1 ← S0 transition because the largest contribution is the HOMO (107a) to LUMO+1 (109a) transition that accounts for only 20.5% of the excitation character.

Table 7. First Excitation Energies in electronvolts (inverse centimeters) of the Ln–Au (Ln = LaIII or LuIII) Models Calculated at the TD-DFT/PBE0/def2-TZVP Levela.

transition energy fb × 10 contributions (%)
La–Au
S1 ← S0 3.822 (30830) 0.425 91a → 92a 97.2
T1 ← S0 3.457 (27880) – 91a → 92a 35.0
Lu–Au
S1 ← S0 4.109 (33140) 0.113 106a → 108a 48.8
      107a → 108a 42.3
T1 ← S0 3.452 (27840) – 107a → 109a 20.5
Open in a new tab
a

The oscillator strength (f) and the dominating excitation character of the excited states are also reported.

b

f is a mixed representation of the oscillator length and velocity.

Figure 4.

Figure 4

Open in a new tab

Most relevant molecular orbitals of the Ln–Au models (Ln = LaIII or LuIII). Color code: C, gray; H, white; Au, yellow; La, sky blue; Lu, green.

4. Conclusions

Our calculations demonstrate that gold(I) and lanthanide(III) atoms can chemically bind when suitable noncoordinating ancillary ligands are chosen. This finding opens the field to a whole new family of heterometallic compounds featuring Au–Ln bonds, which may display excellent photophysical quantum yields and intriguing properties such as bimetallic catalysis and/or single-molecule magnetism. We suggest that the Au–Ln bonds belong to the recently proposed class of charge shift (CS) bonds.75,76 The CS bonding occurs when electron lone pairs or filled semicore subshells exert a strong Pauli repulsion, weakening and even overruling the covalent contribution to the bond as in, e.g., diatomic fluorine. The resonance energy of the mixing of the pure covalent and ionic nature of the wave function acts as the binding force. A feature that characterizes CS bonds is the combination of significant ρe(r) and small positive Inline graphic values in the BCP. A valence bond (VB) analysis should be performed to assess whether the Au–Ln bonds are of CS type. However, we consider that the Au–Ln bonds belong to this category on the basis of the computed QTAIM properties and the fact that the filled 4d10 subshell of the lanthanides may exert a strong Pauli repulsion on the valence 4f orbitals. The proposed nature of the Au–Ln CS bond seems to represent TM–Ln bonding, because analogous intermediate covalent–ionic bonds have been previously described by Butovskii et al.,27,67,68 who identified electrostatic attraction as the driving force of Re–Ln bonds, whereas the basin analysis of the electron localizability indicator (ELI-D) suggested a covalent bond between the metals. Further efforts to synthesize and experimentally characterize these complexes will be attempted and will be reported in due time.

Acknowledgments

The research has been supported by The Academy of Finland through Project 340583. D.B. acknowledges Universidad de La Rioja for the concession of a Margarita Salas postdoctoral scholarship financed by the Spanish Ministerio de Universidades and the European Union-NextGenerationEU program. The authors acknowledge CSC-IT Center for Science, Finland, and the Finnish Grid and Cloud Infrastructure (persistent identifier urn:nbn:fi:research-infras-2016072533) for computational resources. The authors thank Prof. Emer. P. Pyykkö for rewarding discussion and advice about the background of gold–lanthanide chemistry.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c02717.

  • Cartesian coordinates of the Ln–Au, Ln, and Au models (PDF)

The authors declare no competing financial interest.

Supplementary Material

ic2c02717_si_001.pdf (94KB, pdf)

References

  1. Xu H.-B.; Zhang L.-Y.; Ni J.; Chao H.-Y.; Chen Z.-N. Conformation Changes and Luminescent Properties of Au-Ln (Ln = Nd, Eu, Er, Yb) Arrays with 5-Ethynyl-2,2’-Bipyridine. Inorg. Chem. 2008, 47, 10744–10752. 10.1021/ic800733x. [DOI] [PubMed] [Google Scholar]
  2. Ladner L.; Ngo T.; Crawford C.; Assefa Z.; Sykora R. E. Solid-State Photoluminescence Sensitization of Tb3+ by Novel Au2Pt2 and Au2Pt4 Cyanide Clusters. Inorg. Chem. 2011, 50, 2199–2206. 10.1021/ic101836a. [DOI] [PubMed] [Google Scholar]
  3. Thomas R. B.; Smith P. A.; Jaleel A.; Vogel P.; Crawford C.; Assefa Z.; Sykora R. E. Synthesis, Structural, and Photoluminescence Studies of Gd(terpy)(H2O)(NO3)2M(CN)2 (M = Au, Ag) Complexes: Multiple Emissions from Intra- and Intermolecular Excimers and Exciplexes. Inorg. Chem. 2012, 51, 3399–3408. 10.1021/ic2014495. [DOI] [PubMed] [Google Scholar]
  4. Roberts R. J.; Li X.; Lacey T. F.; Pan Z.; Patterson H. H.; Leznoff D. Heterobimetallic lanthanide–gold coordination polymers: structure and emissive properties of isomorphous [nBu4N]2[Ln(NO3)4Au(CN)2] 1-D chains. Dalton Trans 2012, 41, 6992–6997. 10.1039/c2dt30156c. [DOI] [PubMed] [Google Scholar]
  5. Thompson J. R.; Roberts R. J.; Williams V. E.; Leznoff D. B. Birefringent, emissive coordination polymers incorporating bis(benzimidazole)pyridine as an anisotropic building block. CrystEngComm 2013, 15, 9387–9393. 10.1039/c3ce41556b. [DOI] [Google Scholar]
  6. White F.; Pham L. N.; Xiang K. R.; Thomas R.; Vogel P.; Crawford C.; Assefa Z.; Sykora R. E. Synthesis, structures, and photoluminescence properties of lanthanide dicyanoaurates containing dimeric aurophilic interactions. Inorg. Chim. Acta 2014, 414, 240–249. 10.1016/j.ica.2014.02.012. [DOI] [Google Scholar]
  7. Ahern J. C.; Roberts R. J.; Follansbee P.; McLaughlin J.; Leznoff D. B.; Patterson H. H. Structure and Emissive Properties of Heterobimetallic Ln–Au Coordination Polymers: Role of Tb and Eu in Non-aurophilic [nBu4N]2[Ln(NO3)4Au(CN)2] versus Aurophilic Ln[Au(CN)2]3· 3H2O/3D2O Chains. Inorg. Chem. 2014, 53, 7571–7579. 10.1021/ic500890r. [DOI] [PubMed] [Google Scholar]
  8. Roberts R. J.; Ahern J. C.; Patterson H. H.; Leznoff D. B. Ce/Au(CN)2–-Based Coordination Polymers Containing and Lacking Aurophilic Interactions. Eur. J. Inorg. Chem. 2016, 2016, 2082–2087. 10.1002/ejic.201600174. [DOI] [Google Scholar]
  9. Roberts R. J.; Le D.; Leznoff D. Color-Tunable and White-Light Luminescence in Lanthanide-Dicyanoaurate Coordination Polymers. Inorg. Chem. 2017, 56, 7948–7959. 10.1021/acs.inorgchem.7b00735. [DOI] [PubMed] [Google Scholar]
  10. Kumar K.; Stefanćzyk O.; Chorazy S.; Nakabayashi K.; Sieklucka B.; Ohkoshi S.-I. Effect of Noble Metals on Luminescence and Single-Molecule Magnet Behavior in the Cyanido-Bridged Ln–Ag and Ln–Au (Ln = Dy, Yb, Er) Complexes. Inorg. Chem. 2019, 58, 5677–5687. 10.1021/acs.inorgchem.8b03634. [DOI] [PubMed] [Google Scholar]
  11. Zakrzewski J. J.; Sieklucka B.; Chorazy S. Europium(III) Photoluminescence Governed by d8–d10 Heterometallophilic Interactions in Trimetallic Cyanido-Bridged Coordination Frameworks. Inorg. Chem. 2020, 59, 1393–1404. 10.1021/acs.inorgchem.9b03114. [DOI] [PubMed] [Google Scholar]
  12. Hendrich J. M.; White F.; Sykora R. E. Lanthanide dicyanoaurate coordination polymers containing 1,10-phenanthroline: Synthesis, structure, and luminescence. Inorg. Chim. Acta 2021, 527, 120562. 10.1016/j.ica.2021.120562. [DOI] [Google Scholar]
  13. Kaltsoyannis N.; Scott P.. The f elements; Oxford University Press: Oxford, U.K., 1999. [Google Scholar]
  14. Bünzli J.-C. G.; Piguet C. Taking advantage of luminescent lanthanide ions. Chem. Soc. Rev. 2005, 34, 1048–1077. 10.1039/b406082m. [DOI] [PubMed] [Google Scholar]
  15. Colis J. C. F.; Larochelle C.; Staples R.; Herbst-Irmer R.; Patterson H. Structural studies of lanthanide ion complexes of pure gold, pure silver and mixed metal (gold–silver) dicyanides. Dalton Trans 2005, 2, 675–679. 10.1039/B413967D. [DOI] [PubMed] [Google Scholar]
  16. Schmidbaur H.; Schier A. A briefing on aurophilicity. Chem. Soc. Rev. 2008, 37, 1931–1951. 10.1039/b708845k. [DOI] [PubMed] [Google Scholar]
  17. Schmidbaur H.; Schier A. Aurophilic interactions as a subject of current research: an up-date. Chem. Soc. Rev. 2012, 41, 370–412. 10.1039/C1CS15182G. [DOI] [PubMed] [Google Scholar]
  18. Mirzadeh N.; Privér S. H.; Blake A. J.; Schmidbaur H.; Bhargava S. K. Innovative Molecular Design Strategies in Materials Science Following the Aurophilicity Concept. Chem. Rev. 2020, 120, 7551–7591. 10.1021/acs.chemrev.9b00816. [DOI] [PubMed] [Google Scholar]
  19. Pyykkö P. Theoretical Chemistry of Gold. Angew. Chem., Int. Ed. 2004, 43, 4412–4456. 10.1002/anie.200300624. [DOI] [PubMed] [Google Scholar]
  20. Hashmi A. S. K.; Braun I.; Rudolph M.; Rominger F. Gem-Diaurated Gold(III) Complexes: Synthesis, Structure, Aurophilic Interaction, and Catalytic Activity. Organometallics 2012, 31, 644–661. 10.1021/om200946m. [DOI] [PubMed] [Google Scholar]
  21. Wunsch J. F.; Eberle L.; Mullen J. P.; Rominger F.; Rudolph M.; Hashmi A. S. K. Gem-Diaurated Gold(III) Complexes: Synthesis, Structure, Aurophilic Interaction, and Catalytic Activity. Inorg. Chem. 2022, 61, 3508–3515. 10.1021/acs.inorgchem.1c03479. [DOI] [PubMed] [Google Scholar]
  22. Páez-Hernández D.; Muñoz-Castro A.; Arratia-Pérez R. Bonding in gold-rare earth [Au2M] (M = Eu, Yb, Lu) ions. A strong covalent gold-lanthanide bond. Chem. Phys. Lett. 2017, 683, 421–424. 10.1016/j.cplett.2017.03.074. [DOI] [Google Scholar]
  23. Ahmad S.; Shafiq M.; Ahmad R.; Jalali-Asadabadi S.; Ahmad I. Strongly correlated intermetallic rare-earth monoaurides (Ln-Au): Ab-initio study. J. Rare Earths 2018, 36, 1106–1111. 10.1016/j.jre.2018.03.018. [DOI] [Google Scholar]
  24. Ahmad S.; Ahmad R.; Ahmad I. Physical properties and possible applications of gold-based rare earth intermetallics (R-Au): A review. J. Magn. Magn. Matter 2019, 490, 165477. 10.1016/j.jmmm.2019.165477. [DOI] [Google Scholar]
  25. Dahlen M.; Reinfandt N.; Jin C.; Gamer M. T.; Fink K.; Roesky P. W. Hetero-bimetallic Lanthanide-Coinage Metal Compounds Featuring Possible Metal-Metal Interactions in the Excited State. Chem. - Eur. J. 2021, 27, 15128–15136. 10.1002/chem.202102430. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Oelkers B.; Butovskii M. V.; Kempe R. f-Element-metal bonding and the use of bond polarity to build molecular intermetaloids. Chem. - Eur. J. 2012, 18, 13566–13579. 10.1002/chem.201200783. [DOI] [PubMed] [Google Scholar]
  27. Butovskii M. V.; Döring C.; Bezugly V.; Wagner F. R.; Grin Y.; Kempe R. Molecules containing rare-earth atoms solely bonded by transition metals. Nat. Chem. 2010, 2, 741–744. 10.1038/nchem.718. [DOI] [PubMed] [Google Scholar]
  28. TURBOMOLE, ver. 7.5.1; 2021, a development of University of Karlsruhe and Forschungszentrum Karlsruhe GmbH, 1989–2007, TURBOMOLE GmbH, since 2007 (https://www.turbomole.org). [Google Scholar]
  29. Balasubramani S. G.; Chen G. P.; Coriani S.; Diedenhofen M.; Frank M. S.; Franzke Y. J.; Furche F.; Grotjahn R.; Harding M. E.; Hättig C.; Hellweg A.; Helmich-Paris B.; Holzer C.; Huniar U.; Kaupp M.; Marefat Khah A.; Karbalaei Khani S.; Müller T.; Mack F.; Nguyen B. D.; Parker S. M.; Perlt E.; Rappoport D.; Reiter K.; Roy S.; Rückert M.; Schmitz G.; Sierka M.; Tapavicza E.; Tew D. P.; van Wüllen C.; Voora V. K.; Weigend F.; Wodynski A.; Yu J. M. TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations. J. Chem. Phys. 2020, 152, 184107. 10.1063/5.0004635. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Pettersen E. F.; Goddard T. D.; Huang C. C.; Meng E. C.; Couch G. S.; Croll T. I.; Morris J. H.; Ferrin T. E. UCSF ChimeraX: Meeting modern challenges in visualization and analysis. Protein Sci. 2021, 30, 70–82. 10.1002/pro.3943. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Perdew J. P.; Burke K.; Ernzerhof M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. 10.1103/PhysRevLett.77.3865. [DOI] [PubMed] [Google Scholar]
  32. Perdew J. P.; Ernzerhof M.; Burke K. Rationale for mixing exact exchange with density functional approximations. J. Chem. Phys. 1996, 105, 9982. 10.1063/1.472933. [DOI] [Google Scholar]
  33. Adamo C.; Barone V. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110, 6158–6170. 10.1063/1.478522. [DOI] [Google Scholar]
  34. Weigend F.; Ahlrichs R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297–3305. 10.1039/b508541a. [DOI] [PubMed] [Google Scholar]
  35. Gulde R.; Pollak P.; Weigend F. Error-Balanced Segmented Contracted Basis Sets of Double-ζ to Quadruple-ζ Valence Quality for the Lanthanides. J. Chem. Theory Comput. 2012, 8, 4062–4068. 10.1021/ct300302u. [DOI] [PubMed] [Google Scholar]
  36. Grimme S.; Antony J.; Ehrlich S.; Krieg H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104. 10.1063/1.3382344. [DOI] [PubMed] [Google Scholar]
  37. Grimme S.; Ehrlich S.; Goerigk L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011, 32, 1456–1465. 10.1002/jcc.21759. [DOI] [PubMed] [Google Scholar]
  38. Treutler O.; Ahlrichs R. Efficient molecular numerical integration schemes. J. Chem. Phys. 1995, 102, 346–354. 10.1063/1.469408. [DOI] [Google Scholar]
  39. Eichkorn K.; Treutler O.; Öhm H.; Häser M.; Ahlrichs R. Auxiliary basis sets to approximate Coulomb potentials. Chem. Phys. Lett. 1995, 242, 652–660. 10.1016/0009-2614(95)00838-U. [DOI] [Google Scholar]
  40. Eichkorn K.; Weigend F.; Treutler O.; Ahlrichs R. Auxiliary basis sets for main row atoms and transition metals and their use to approximate Coulomb potentials. Theor. Chem. Acc. 1997, 97, 119–124. 10.1007/s002140050244. [DOI] [Google Scholar]
  41. Weigend F. Accurate Coulomb-fitting basis sets for H to Rn. Phys. Chem. Chem. Phys. 2006, 8, 1057–1065. 10.1039/b515623h. [DOI] [PubMed] [Google Scholar]
  42. Andrae D.; Häussermann U.; Dolg M.; Stoll H.; Preuss H. Energy-adjusted ab initio pseudopotentials for the second and third row transition elements. Theor. Chim. Acta 1990, 77, 123–141. 10.1007/BF01114537. [DOI] [Google Scholar]
  43. Deglmann P.; May K.; Furche F.; Ahlrichs R. Nuclear second analytical derivative calculations using auxiliary basis set expansion. Chem. Phys. Lett. 2004, 384, 103–107. 10.1016/j.cplett.2003.11.080. [DOI] [Google Scholar]
  44. Häser M.; Ahlrichs R. Improvements on the direct SCF method. J. Comput. Chem. 1989, 10, 104–111. 10.1002/jcc.540100111. [DOI] [Google Scholar]
  45. Weigend F.; Häser M. RI-MP2: first derivatives and global consistency. Theor. Chem. Acc. 1997, 97, 331–340. 10.1007/s002140050269. [DOI] [Google Scholar]
  46. Weigend F.; Häser M.; Patzelt H.; Ahlrichs R. RI-MP2: optimized auxiliary basis sets and demonstration of efficiency. Chem. Phys. Lett. 1998, 294, 143–152. 10.1016/S0009-2614(98)00862-8. [DOI] [Google Scholar]
  47. Hättig C.; Hellweg A.; Köhn A. Distributed memory parallel implementation of energies and gradients for second-order Møller–Plesset perturbation theory with the resolution-of-the-identity approximation. Phys. Chem. Chem. Phys. 2006, 8, 1159–1169. 10.1039/b515355g. [DOI] [PubMed] [Google Scholar]
  48. Jansen H. B.; Ros P. Non-Empirical Molecular Orbital Calculations on the Protonation of Carbon Monoxide. Chem. Phys. Lett. 1969, 3, 140–143. 10.1016/0009-2614(69)80118-1. [DOI] [Google Scholar]
  49. Boys S. F.; Bernardi F. The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 1970, 19, 553–566. 10.1080/00268977000101561. [DOI] [Google Scholar]
  50. Zhao L.; von Hopffgarten M.; Andrada D. M.; Frenking G. Energy decomposition analysis. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2018, 8, 1345. 10.1002/wcms.1345. [DOI] [Google Scholar]
  51. Bader R. F. W. A quantum theory of molecular structure and its applications. Chem. Rev. 1991, 91, 893–928. 10.1021/cr00005a013. [DOI] [Google Scholar]
  52. Bader R. F. W.; MacDougall P. J.; Lau C. D. H. Bonded and nonbonded charge concentrations and their relation to molecular geometry and reactivity. J. Am. Chem. Soc. 1984, 106, 1594–1605. 10.1021/ja00318a009. [DOI] [Google Scholar]
  53. Lu T.; Chen Q. Interaction Region Indicator: A Simple Real Space Function Clearly Revealing Both Chemical Bonds and Weak Interactions. Chem.: Methods 2021, 1, 231–239. 10.1002/cmtd.202100007. [DOI] [Google Scholar]
  54. Lu T.; Chen F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33, 580–592. 10.1002/jcc.22885. [DOI] [PubMed] [Google Scholar]
  55. Humphrey W.; Dalke A.; Schulten K. VMD: visual molecular dynamics. J. Mol. Graph. 1996, 14, 33–38. 10.1016/0263-7855(96)00018-5. [DOI] [PubMed] [Google Scholar]
  56. Furche F.; Rappoport D.. Computational Photochemistry. In Computational and Theoretical Chemistry; Olivucci M., Ed.; Elsevier: Amsterdam, 2005; Vol. 16, Chapter III. [Google Scholar]
  57. Casida M. E.; Huix-Rotllant M. Progress in Time-Dependent Density-Functional Theory. Annu. Rev. Phys. Chem. 2012, 63, 287–323. 10.1146/annurev-physchem-032511-143803. [DOI] [PubMed] [Google Scholar]
  58. Bauernschmitt R.; Ahlrichs R. Treatment of electronic excitations within the adiabatic approximation of time dependent density functional theory. Chem. Phys. Lett. 1996, 256, 454–464. 10.1016/0009-2614(96)00440-X. [DOI] [Google Scholar]
  59. Bauernschmitt R.; Ahlrichs R. Stability analysis for solutions of the closed shell Kohn-Sham equation. J. Chem. Phys. 1996, 104, 9047–9052. 10.1063/1.471637. [DOI] [Google Scholar]
  60. Bauernschmitt R.; Häser M.; Treutler O.; Ahlrichs R. Calculation of excitation energies within time-dependent density functional theory using auxiliary basis set expansions. Chem. Phys. Lett. 1997, 264, 573–578. 10.1016/S0009-2614(96)01343-7. [DOI] [Google Scholar]
  61. Pyykkö P.; Atsumi M. Molecular Single-Bond Covalent Radii for Elements 1–118. Chem. - Eur. J. 2009, 15, 186–197. 10.1002/chem.200800987. [DOI] [PubMed] [Google Scholar]
  62. Pyykkö P. Molecular Single-Bond Covalent Radii for Elements 1–118. J. Phys. Chem. A 2015, 119, 2326–337. 10.1021/jp5065819. [DOI] [PubMed] [Google Scholar]
  63. Cordero B.; Gómez V.; Platero-Prats A. E.; Revés M.; Echeverría J.; Cremades E.; Barragán F.; Alvarez S. Covalent radii revisited. Dalton Trans 2008, 2832–2838. 10.1039/b801115j. [DOI] [PubMed] [Google Scholar]
  64. Allred A. L. Electronegativity values from thermochemical data. J. Inorg. Nucl. Chem. 1961, 17, 215–221. 10.1016/0022-1902(61)80142-5. [DOI] [Google Scholar]
  65. Vlaisavljevich B.; Miró P.; Cramer C. J.; Gagliardi L.; Infante I.; Liddle S. T. On the Nature of Actinide- and Lanthanide-Metal Bonds in Heterobimetallic Compounds. Chem. - Eur. J. 2011, 17, 8424–8433. 10.1002/chem.201100774. [DOI] [PubMed] [Google Scholar]
  66. Frenking G.; Krapp A. Unicorns in the World of Chemical Bonding Models. J. Comput. Chem. 2007, 28, 15–24. 10.1002/jcc.20543. [DOI] [PubMed] [Google Scholar]
  67. Butovskii M. V.; Tok O. L.; Wagner F. R.; Kempe R. Bismetallocenes: Lanthanoid–Transition-Metal Bonds through Alkane Elimination. Angew. Chem., Int. Ed. 2008, 47, 6469–6472. 10.1002/anie.200800407. [DOI] [PubMed] [Google Scholar]
  68. Butovskii M. V.; Oelkers B.; Bauer T.; Bakker J. M.; Bezugly V.; Wagner F. R.; Kempe R. Lanthanoid–Transition-Metal Bonding in Bismetallocenes. Chem. - Eur. J. 2014, 20, 2804–2811. 10.1002/chem.201304125. [DOI] [PubMed] [Google Scholar]
  69. de Silva P.; Corminboeuf C. Simultaneous Visualization of Covalent and Noncovalent Interactions Using Regions of Density Overlap. J. Chem. Theory Comput. 2014, 10, 3745–3756. 10.1021/ct500490b. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. López-de-Luzuriaga J. M.; Monge M.; Olmos M. E.; Rodríguez-Castillo M.; Sorroche A. Computational prediction of Au(I)–Pb(II) bonding in coordination complexes and study of the factors affecting the formation of Au(I)–E(II) (E = Ge, Sn, Pb) covalent bonds. Phys. Chem. Chem. Phys. 2021, 23, 10174–10183. 10.1039/D1CP00325A. [DOI] [PubMed] [Google Scholar]
  71. Yang X.; Burns C. P.; Nippe M.; Hall M. B. Unsupported Lanthanide–Transition Metal Bonds: Ionic vs Polar Covalent?. Inorg. Chem. 2021, 60, 9394–9401. 10.1021/acs.inorgchem.1c00285. [DOI] [PubMed] [Google Scholar]
  72. Bianchi R.; Gervasio G.; Marabello D. Experimental electron density analysis of Mn2(CO)10: metal-metal and metal-ligand bond characterization. Inorg. Chem. 2000, 39, 2360–2366. 10.1021/ic991316e. [DOI] [PubMed] [Google Scholar]
  73. Laporte O.; Meggers W. F. Some Rules of Spectral Structure. J. Opt. Soc. Am. 1925, 11, 459–463. 10.1364/JOSA.11.000459. [DOI] [Google Scholar]
  74. Latva M.; Takalo H.; Mukkala V.-M.; Matachescu C.; Rodríguez-Ubis J. C.; Kankare J. Correlation between the lowest triplet state energy level of the ligand and lanthanide(III) luminescence quantum yield. J. Lumin. 1997, 75, 149–169. 10.1016/S0022-2313(97)00113-0. [DOI] [Google Scholar]
  75. Shaik S.; Danovich D.; Galbraith J. M.; Bräida B.; Wu W.; Hiberty P. C. Charge-Shift Bonding: a New and Unique Form of Bonding. Angew. Chem., Int. Ed. 2020, 59, 984–1001. 10.1002/anie.201910085. [DOI] [PubMed] [Google Scholar]
  76. Joy J.; Danovich D.; Kaupp M.; Shaik S. Covalent vs Charge-Shift Nature of the Metal–Metal Bond in Transition Metal Complexes: A Unified Understanding. J. Am. Chem. Soc. 2020, 142, 12277–12287. 10.1021/jacs.0c03957. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ic2c02717_si_001.pdf (94KB, pdf)

Articles from Inorganic Chemistry are provided here courtesy of American Chemical Society

RESOURCES