Syntheses of Dioxygenyl Salts by Photochemical Reactions in Liquid Anhydrous Hydrogen Fluoride: X-ray Crystal Structures of α- and β-O₂Sn₂F₉, O₂Sn₂F₉·0.9HF, O₂GeF₅·HF, and O₂[Hg(HF)]₄(SbF₆)₉

Abstract

By treating gaseous, liquid, or solid fluorides with UV-photolyzed O₂/F₂ mixtures and by treating solid oxides with UV-photolyzed F₂ (or O₂/F₂ mixtures) in liquid anhydrous HF at ambient temperature, we investigated the possibility of the preparation of O₂M^IIIF₄ (M = B, Fe, Co, Ag), O₂M^IVF₅ (M = Ti, Sn, Pb), (O₂)₂M^IVF₆ (M = Ti, Ge, Sn, Pb, Pd, Ni, Mn), O₂M^IV₂F₉ (M = Sn), O₂M^VF₆ (M = As, Sb, Au, Pt), O₂M^V₂F₁₁ (M = Pt), O₂M^VIF₇ (M = Se), (O₂)₂M^VIF₈ (M = Mo, W), and O₂M^VIIF₈ (M = I). The approach has been successful in the case of previously known O₂BF₄, O₂MF₆ (M = As, Sb, Au; Pt), O₂GeF₅, and (O₂)₂(Ti₇F₃₀). Novel compounds O₂GeF₅·HF, α-O₂Sn₂F₉ (1-D), and the HF-solvated and nonsolvated forms of β-O₂Sn₂F₉ (2-D) were synthesized and their crystal structures determined using single-crystal X-ray diffraction. The crystal structures of all of these materials arise from the condensation of octahedral MF₆ (M = Ge, Sn) units. The anion in the crystal structure of O₂GeF₅·HF is comprised of infinite ([GeF₅]⁻)_∞ chains of GeF₆ octahedra that share common vertices. The HF molecules and O₂⁺ cations are located between the chains. The crystal structure of α-O₂SnF₉ (1-D) is constructed from [O₂]⁺ cations and polymeric ([Sn₂F₉]⁻)_∞ anions which appear as two parallel infinite chains comprised of SnF₆ units, where each SnF₆ unit of one chain is connected to a SnF₆ unit of the second chain through a shared fluorine vertex. The single-crystal structure determination of [O₂][Sn₂F₉]·0.9HF reveals that it is comprised of two-dimensional ([Sn₂F₉]⁻)_∞ grids with [O₂]⁺ cations and HF molecules located between them. The 2-D grids have a wavelike conformation. The ([Sn₂F₉]⁻)_∞ layer contains both six- and seven-coordinated Sn(IV) atoms that are interconnected by bridging fluorine atoms. A new, more complex [O₂]⁺ salt, O₂[Hg(HF)]₄[SbF₆]₉, was prepared. In its crystal structure, the Hg atoms bridge to SbF₆ units to form a 3-D framework. The O₂⁺ cations are located inside the voids while the HF molecules are bound to Hg atoms through the F atom. Attempts to prepare several chlorine analogues of O₂⁺ fluorine salts (i.e., O₂TiCl₅ and O₂MCl₆ (M = Nb, Sb)) failed.

Short abstract

Reactions between fluorides and/or oxides and UV-irradiated F₂ and/or F₂/O₂ mixtures were carried out in anhydrous hydrogen fluoride at ambient temperature to prepare O₂⁺ salts. The crystal structures of O₂GeF₅·HF and O₂GeF₅ consist of infinite polymeric ([GeF₅]⁻)_∞ anions. The O₂Sn₂F₉ salt exhibits polymorphism consisting of a 1-D phase built from double chainlike ([Sn₂F₉]⁻)_∞ anions and a 2-D phase built from layerlike anions. The latter also exists as a solvated form O₂Sn₂F₉·nHF. The crystal structure of O₂[Hg(HF)]₄(SbF₆)₉ is isotypic to that of H₃O[Cd(HF)]₄(SbF₆)₉. The Hg atoms are bridged by SbF₆ groups forming a 3-D framework with O₂⁺ cations located inside the voids. The HF molecules are bound to Hg atoms through the F atom.

Introduction

Dioxygenyl salts are useful reagents for the oxidation of organic compounds to the corresponding cation radicals.^1,2 The O₂AsF₆ and O₂SbF₆ are capable of oxidizing C₆F₆ and C₅F₅N to C₆F₆⁺, yielding [C₆F₆]⁺[MF₆]⁻ (M = As, Sb)^3,4 or [C₆F₅N]⁺[MF₆]⁻ (M = As),⁵ respectively. The preparations of substituted and hydrogen-containing fluoroaryl cations (i.e., [C₆F₅X]⁺, X = H, CF₃ or C₆F₅; [1,4-C₆F₄(CF₃)₂]⁺; [2,3,5,6-C₆F₄X₂]⁺, X = H or CF₃; [2,4,6-C₆H₃F₃]⁺; [1,2,4,5-C₆H₂Cl₄]⁺) as [AsF₆]⁻, [SbF₆]⁻, or [Sb₂F₁₁]⁻ salts also have been reported.^6,7 Other examples include the preparation of tertiary amine cation radicals⁸ and the oxidations of N,N,N,N-tetramethyl-p-phenylenediamine, 1,4-diazabicyclo[2.2.2]octane, and 1,5-dithiacyclooctane to the corresponding radical cations as shown by EPR spectroscopy.⁹ The reaction of (CF₃)₂NO with O₂SbF₆ produces CF₃ radicals at low temperature.¹⁰ Displacement reactions between O₂MF₆ and suitable amphoteric molecules produce free O₂F radicals which generate atomic fluorine in situ upon decomposition.¹¹ A one-step reaction between carbon monoxide and dioxygenyl salts yields oxalyl fluoride [FC(O)C(O)F].¹² The removal of radon and radioactive noble gas isotopes of xenon from contaminated atmospheres through the use of O₂SbF₆ was also studied.^13,14 The reactivity of azides toward various dioxygenyl salts was investigated in the scope of research on highly energetic materials.¹⁵

The first dioxygenyl salt, O₂PtF₆, was reported by Bartlett and Lohmann in 1962.^16,17 It was initially erroneously identified as PtOF₄,¹⁸ which is not surprising given that the [O₂]⁺ cation as the [PtF₆]⁻ anion were unknown at that time. It now appears that the dioxygenyl salt, O₂BF₄, may have been prepared at the same time, although the nature of this material was not elucidated at that time.¹⁹ After more than half a century, the number of known [O₂]⁺ salts is still limited to approximately 25 examples.^20,21 Almost two-thirds of them are O₂MF₆ and O₂M₂F₁₁ (M = M⁵⁺) compounds. In addition to O₂MF₆ (M = Sb,²² Au,²²⁻²⁵ Rh,²⁵ Ru,^22,26 Pt^22,27), only the crystal structures of O₂BF₄,²⁸ (O₂)₂Ti₇F₃₀,²⁹ O₂Mn₂F₉,³⁰ O₂Ni(AsF₆)₃,²⁰ and O₂(H₃Pd₂F₁₂)²¹ have been reported.

A convenient way to prepare dioxygenyl fluoride salts is by UV photolysis of gaseous, liquid, or solid fluorides with O₂/F₂ and by UV photolysis of oxides with F₂ (or O₂/F₂ mixtures) in liquid anhydrous HF at ambient temperature.³¹ Applying this general method, we systematically investigated the possibility of the preparation of new or already known O₂M^IIIF₄, O₂M^IVF₅, (O₂)₂M^IVF₆, O₂M^IV₂F₉, O₂M^VF₆, O₂M₂^VF₁₁, O₂M^VIF₇, (O₂)₂M^VIF₈, and O₂M^VIIF₈ compounds. We also investigated the possibility of preparing new, more complex [O₂]⁺/metal mixed-cation salts of hexafluoridoantimonate(V). The results of this study are described in the present work.

Results and Discussion

Reactions between the corresponding fluoride, oxides, and/or metals and UV-irradiated F₂ or F₂/O₂ mixtures were carried out in anhydrous hydrogen fluoride (aHF) at ambient temperature (Table 1). Two additional experiments were done in the absence of a solvent. The presence of O₂⁺ in the solid state is easily detected by Raman spectroscopy.^20,24,47

Table 1. Products Observed Resulting from the Reactions of the Corresponding Fluorides, Oxides, and/or Metals and UV-Irradiated F₂ or F₂/O₂ Mixtures Carried out in aHF at Ambient Temperature.

desired product	reactant 1	reactant 2	observed productsa
O2MIIIF4	BF3	O2/F2	O2BF4b
O2MIIIF4	FeF3	O2/F2	FeF3
O2MIIIF4	CoF2	O2/F2	CoF3
O2MIIIF4	AgF2	O2/F2	Ag3F8
O2MIVF5	TiO2	F2	(O2)2Ti7F30
O2MIVF5	SnO2	F2	O2Sn2F9·0.9HF, α-O2Sn2F9 (1-D)c
O2MIVF5	PbO2	F2	PbF4
(O2)2MIVF6	TiO2	O2/F2	(O2)2Ti7F30
(O2)2MIVF6	SnO2	O2/F2	α-O2Sn2F9 (1-D), β-O2Sn2F9 (2-D), O2Sn2F9·0.9HFc
(O2)2MIVF6	PbO2	O2/F2	PbF4
(O2)2MIVF6	GeF4	O2/F2d	O2GeF5
(O2)2MIVF6	GeF4	O2/F2	O2GeF5·HFe
(O2)2MIVF6	Pd2F6	O2/F2	O2PdF5/undefined [O2+]-saltf
(O2)2MIVF6	NiF2	O2/F2	NiF2/NiF2+x
(O2)2MIVF6	MnF2	O2/F2	undefined [O2+]-salt
O2M2IVF9	SnO2 + SnF4	F2	α-O2Sn2F9 (1-D), O2Sn2F9·0.9HFc
O2MVF6	AsF5	O2/F2	O2AsF6g
O2MVF6	SbF3/SbF5	O2/F2	O2SbF6g
O2MVF6	AuF3	O2/F2	O2AuF6g
O2MVF6	Pt	O2/F2	O2PtF6/Pt
O2M2VF11	PtO2, Pt	F2	no reaction
O2MVIF7	SeO2	F2	SeF6 (?)h
(O2)2MVIF8	MoO3	O2/F2	MoOF4
(O2)2MVIF8	WO3	O2/F2	WF6 (?)i
(O2)2MVIF8	WF6	O2/F2c	WF6 (?)i
O2MVIIF8	IF5	O2/F2	IF7 (?)j
O2MVIIF8	IF5	O2/F2c	IF7 (?)j

^aProducts were identified by Raman spectroscopy and/or single-crystal X-ray diffraction analysis. There is always a possibility that phases present in minor amounts were overlooked.

^bReference (20).

^cTwo phases with the same empirical chemical formula O₂SnF₉ were obtained. The anion of the first one has a chainlike structure and the second one a layerlike structure. To distinguish between them, the former is designated as 1-D (one-dimensional) and the latter as 2-D (two-dimensional). Additionally, there is a third phase, that is, the HF solvated form of 2-D O₂Sn₂F₉ (i.e., O₂Sn₂F₉·0.9HF).

^dFormed in the absence of aHF solvent.

^eSingle crystals were grown from saturated HF solutions at T < −10 °C.

^fThe attempt to grow single crystals from an orange solution at T < −5 °C resulted in an orange-red undefined product of very poor crystallinity, whereas the insoluble material corresponded to a mixture of O₂PdF₅ and an undefined [O₂⁺]-salt as shown by Raman spectroscopy.

^gReference (31).

^hWhen isolation was attempted at room temperature (RT), everything pumped away; SeF₆ is a colorless gas at RT.

ⁱWhen isolation was attempted at RT, everything pumped away; WF₆ is a colorless liquid at RT.

^jWhen isolation was attempted at RT, everything pumped away; IF₇ is a colorless gas at RT.

Attempted Syntheses of O₂M^IIIF₄ (M = B, Fe, Co, Ag)

The reported syntheses of O₂BF₄ include the reaction between BF₃ and O₂F₂.²⁸ The resulting O₂BF₄ salt decomposes above 0 °C. When the synthesis is done in liquid aHF in a FEP reaction vessel (Table 1), the volatile compounds can be easily pumped away at low temperature and pure O₂BF₄ can be recovered in a quantitative yield (Figure S1, see the Supporting Information).

Attempts to prepare O₂⁺ analogues of KMF₄ (M = Fe, Co)³² failed (Table 1). Only the corresponding trifluorides were recovered after isolation at room temperature.

An attempt to prepare the previously reported O₂AgF₄ salt³³ also failed, although O₂AgF₄ is claimed to have been obtained in some reactions of O₂F₂ with silver compounds in ClF₅ solution. The reaction between AgF₂ and a UV-irradiated mixture of F₂/O₂ (Table 1) resulted in Ag₃F₈ (i.e., the mixed-oxidation-state Ag[AgF₄]₂ fluoride³⁴ (Figure S2, see the Supporting Information).

Attempted Syntheses of O₂M^IVF₅ (M = Ti, Sn, Pb)

Two examples of O₂M^IVF₅ compounds are known from the literature. The first is O₂GeF₅ prepared by UV photolysis of a GeF₄/O₂/F₂ mixture in quartz at −78 °C, which is unstable at 25 °C.³⁵ The second is O₂PdF₅, isolated from a deep orange solution presumed to contain (O₂)₂PdF₆ dissolved in aHF.³⁶

Since they already contain the required n(O)/n(M) = 2:1 molar ratio as in O₂M^IVF₅, the corresponding dioxides MO₂ (M = Ti, Sn, Pb) were used as starting materials (Table 1). The reaction between TiO₂ and F₂ in the presence of UV-light in aHF yielded only the previously known (O₂)₂(Ti₇F₃₀) salt,²⁹ whereas in the case of PbO₂, only PbF₄ was recovered (Table 1 and Figure S3, see the Supporting Information). An attempt to synthesize O₂SnF₅ in a similar manner resulted in two phases of the novel O₂[Sn₂F₉] compound (Figure S3, see Supporting Information).

Attempted Syntheses of (O₂)₂M^IVF₆ (M = Ge, Ti, Sn, Pb, Pd, Ni, Mn)

Dioxygenyl salts containing doubly charged mononuclear counterions (i.e., [MF₆]^2–, M = Mn, Ni) were prepared by metathetical reactions between 2O₂SbF₆ and Cs₂MF₆ (M = Mn, Ni) in aHF solution at −45 °C.³⁷ The resulting compounds are marginally stable up to about 10 °C. Addition of a solution of a highly soluble salt A₂PdF₆ (A = K, Cs) in aHF to a solution of O₂AsF₆ in aHF at −30 °C yielded precipitates of AAsF₆ and a deep orange solution presumed to contain (O₂)₂PdF₆.³⁶ Attempts to isolate the latter salt by removal of aHF at −60 °C always resulted in the O₂ and F₂ loss and the recovery of O₂PdF₅. However, further crystallizations at T < −70 °C resulted in the growth of single crystals of [O₂][H₃Pd₂F₁₂].²¹ It has been claimed that (O₂)₂SnF₆ was obtained by the reaction of O₂F₂ with SnF₄.³⁸ However, this reaction is of low yield and poor reproducibility.

The products of the reactions between MO₂ (M = Ti, Sn, Pb) and UV-irradiated F₂ in the presence of an excess of O₂ and in aHF solvent were identical to those obtained in attempts to prepare O₂MF₅ compounds where no additional O₂ was used (Table 1). Reactions with TiO₂ gave (O₂)₂(Ti₇F₃₀)²⁹ and reactions with SnO₂ yielded [Sn₂F₉]⁻ salts. In the case of PbO₂, only PbF₄ was recovered.

The reaction between GeF₄ and F₂/O₂ exposed to UV light in the absence of solvent (Table 1) resulted in the previously known O₂GeF₅ salt (Figure S4, see the Supporting Information).³⁵ When the reaction was carried out in liquid HF and single crystals were grown from a saturated HF solution at T < −10 °C, the HF solvated form of O₂GeF₅ was obtained (i.e., O₂GeF₅·HF). A similar attempt to grow single crystals from an orange solution prepared by reaction of Pd₂F₆ and a UV-irradiated F₂/O₂ mixture in aHF, and further crystallization at T < −5 °C, resulted in an orange-red, poorly crystalline product that was unsuitable for single-crystal X-ray diffraction measurements, and the insoluble material corresponded to O₂PdF₅³⁶ and an undefined [O₂⁺]-salt (Figure S5, see the Supporting Information).

When the NiF₂/F₂/O₂ mixture was irradiated with UV light, aHF-insoluble, pale yellow-green NiF₂ turned black on the surface. This suggests that NiF₂ is partially fluorinated to NiF_2+x (x ≤ 1). The same phenomenon was observed when NiF₂ was exposed to UV-irradiated F₂ in aHF in the absence of O₂.³¹ The Raman spectrum of the product resulting from the reaction of MnF₂ with F₂/O₂ in the presence of a UV source in aHF showed a vibrational band at 1827 cm^–1, which could be assigned to O₂⁺ (Figure S6, see the Supporting Information). The ν(O₂⁺) band occurs at 1805 cm^–1 in the Raman spectrum of (O₂)₂MnF₆,³⁷ and that of O₂Mn₂F₉³⁰ at 1838 cm^–1. In addition, during the syntheses of MnF₄ by photodissociated F₂ and MnF₂ or MnF₃ in aHF, a broad band at 1834 cm^–1 was sometimes observed.³⁹ This indicates that, in addition to (O₂)₂MnF₆ and O₂Mn₂F₉, at least two more O₂⁺/Mn⁴⁺ fluoride salts must exist, although their compositions remain an open question.

Attempted Syntheses of O₂M^IV₂F₉ (M = Sn)

There is only one previously known example of an O₂M^IV₂F₉ salt, i.e., O₂Mn₂F₉, which was first prepared by treating MnO₂ or MnF_x (x = 2, 3, 4) with an F₂/O₂ mixture under quite drastic conditions (p(F₂)/p(O₂) ≈ 300–3500 atm, T ≈ 300–550 °C).³⁰

In this work, we were able to prepare an analogue of an O₂M^IV₂F₉ compound with tin by carrying out a chemical reaction between SnO₂, SnF₂ (molar ratio 1:1), and UV-irradiated F₂ in liquid aHF at ambient temperature (Figure S7, see Supporting Information).

Attempted Syntheses of O₂M^VF₆ (M = As, Sb, Au, Pt)

Because the O₂M^VIF₆ salts are among the most studied O₂⁺ salts,^17,22−27 we did not place a great deal of emphasis on further examples. The O₂M^VIF₆ (M = As, Sb, Au) salts can be conveniently prepared by treating MF₃ (M = As, Sb, Au) or MF₅ (M = As, Sb) with a UV-irradiated F₂/O₂ mixture in aHF (Table 1).³¹ Since AsF₅ is a gas and SbF₅ is a liquid at room temperature, O₂AsF₆ and O₂SbF₆ can be prepared photochemically (even by exposure to daylight⁴⁰) directly from the corresponding binary fluorides, O₂, and F₂ in the absence of HF^22,41 or by other approaches (using O₂F₂⁴² or high-temperature syntheses^22,43). Therefore, the synthetic method is a matter of choice. When the syntheses are done in liquid aHF in FEP reaction vessels, the volatiles can be easily removed at low or ambient temperature and pure O₂MF₆ (M = As, Sb, Au) salts are recovered in quantitative yields. The attempt to prepare O₂PtF₆ by treating Pt metal with a UV-irradiated O₂/F₂ mixture in aHF was only partially successful. The desired compound was formed (Figure S8, see the Supporting Information), but the yield was low. A much more facile synthesis of pure O₂PtF₆ without the demanding synthesis of PtF₆, or the use of high-pressure fluorination, has recently been reported.⁴⁴

Attempted Syntheses of O₂M^V₂F₁₁ (M = Pt)

In addition to O₂M^VIF₆, O₂M^V₂F₁₁ is the second most prevalent group of O₂⁺ salts that is described in the literature.^41,45−47 Based on vibrational spectroscopic data, their structures consist of O₂⁺ cations and dimeric M₂F₁₁^– anions.⁴⁷ The only crystal structure that has been determined from single-crystal X-ray diffraction data for this class of O₂⁺ salts is O₂Pt₂F₁₁, but a complete structure determination has never been published.⁴⁸ Our attempt to prepare O₂Pt₂F₁₁ by reaction between PtO₂/Pt (molar ratio 1:1) and UV-irradiated F₂ in aHF failed (Table 1).

Attempted Syntheses of O₂M^VIF₇ (M = Se), (O₂)₂M^VIF₈ (M = Mo, W), and O₂M^VIIF₈ (M = I)

There is no indication in the literature for the formation of [SeF₇]⁻, whereas [MF₇]⁻ (M = W, Mo) are well-known.⁴⁹ Tungsten hexafluoride can add two fluoride anions to form [WF₈]^2–, but [MoF₈]^2– has not yet been observed.⁴⁹ The [IF₈]⁻ anion has been observed in the crystal structure of [NO(NOF)₂][IF₈].⁵⁰ There are reports of the syntheses of NOMF₇ (M = Mo, W) and (NO)₂WF₈.⁵¹ A brief mention of analogous O₂⁺ salts is limited to the possible existence of O₂MoF₇ and O₂WF₇,³⁸ although these data have not been confirmed. All of our attempts to synthesize O₂⁺ salts of the [M^VIF₇]⁻ (M = Se), [M^VIF₈]^2– (M = Mo, W) or [M^VIIF₈]⁻ (M = I) anions failed (Table 1). In each case, nothing remained in the reaction vessels after volatile compounds had been removed under vacuum at room temperature. It can be assumed that the WF₆ (starting material or formed by fluorination of WO₃) and IF₇ (formed by fluorination of IF₅) were simply pumped off at room temperature. The chemical reaction between MoO₃ and the UV-irradiated F₂/O₂ mixture resulted in a colorless solution from which a colorless material was recovered. Its Raman spectrum was identical to the reported Raman spectrum of solid MoOF₄, which was obtained by cooling its melt (Figure S9, see the Supporting Information).⁵² A very weak vibrational band at 1850 cm^–1 was sometimes observed, indicating the presence of an unknown O₂⁺ salt.

Attempted Syntheses of (O₂)₂Hg₂F(SbF₆)₅ and (O₂)₂Hg₂(SbF₆)₆

In the case of more complex O₂⁺ salts, only O₂Ni(AsF₆)₃ has been reported thus far.²⁰ Because the synthesis and crystal data of (O₂)₂Hg₂F(SbF₆)₅⁵³ have never been published, we were interested in determining if it is possible to prepare this compound in liquid aHF by reaction between O₂SbF₆, HgF₂, and SbF₅ (formed in situ by fluorination of SbF₃ with elemental F₂) in the required molar ratio, 2:2:3. We also explored the possibility of preparing (O₂)₂Hg₂(SbF₆)₆ by using a larger amount of SbF₅ [n(O₂SbF₆)/n(HgF₂)/n(SbF₅) = 2:2:4]. In both cases, the growth of crystals from saturated aHF solutions resulted in single crystals of O₂SbF₆, Hg(HF)(SbF₆)₂,⁵⁴ and previously unknown O₂SbF₆·([Hg(HF)][SbF₆]₂)₄ (better formulated as O₂[Hg(HF)]₄[SbF₆]₉). The pure phase can be obtained when the appropriate starting ratio [n(O₂SbF₆)/n(HgF₂)/n(SbF₅) = 1:4:8] is used (Figure S10, see the Supporting Information).

Attempted Syntheses of O₂M^VCl₆, O₂M^IVCl₅, and (O₂)₂SO₄

Since all known O₂⁺ salts are based on fluorides, it is clear that nonoxidizable anions are required to stabilize O₂⁺. We were interested in determining what would happen when SbCl₅/Cl₂/O₂, TiCl₄/Cl₂/O₂/HCl, and NbCl₅/Cl₂/O₂/HCl mixtures are exposed to UV-light. Both SbCl₅ and TiCl₄ are liquids, but NbCl₅ is a solid at room temperature. In the cases of TiCl₄ and SbCl₅, the formation of yellow solids was observed (Figure S11, see the Supporting Information). The absence of vibrational bands in the 1800–1870 cm^–1 region of the Raman spectra of the isolated solids showed that no O₂⁺ salts were formed. This was also the case when NbCl₅ was used as the starting material. Therefore, the products were not investigated further.

The relative oxidizing strength of O₂⁺ has been estimated to be close to that of Ag²⁺_(solv) (i.e., cationic Ag²⁺ in aHF solution).⁵⁵ A metathetical reaction between K₂SO₄ and Ag(SbF₆)₂ in aHF yields Ag^IISO₄.⁵⁶ Our similar attempt to prepare (O₂)₂SO₄ by a metathetical reaction between K₂SO₄ and 2O₂SbF₆ in aHF also failed. Only KSbF₆ was recovered upon isolation of the solid at −15 °C.

Crystal Structures of O₂SnF₉ (1-D and 2-D), O₂SnF₉·0.9HF, O₂GeF₅·HF, and O₂[Hg(HF)]₄(SbF₆)₉

The corresponding crystal data and refinement results for α- and β-O₂SnF₉ (1-D and 2-D), O₂SnF₉·0.9HF, O₂GeF₅·HF, and O₂[Hg(HF)]₄(SbF₆)₉ are summarized in Table 2, and the unit cell parameters of O₂GeF₅ are also provided.

Table 2. Summary of Crystal Data and Refinement Results of α- and β-O₂SnF₉ (1-D, 2-D), O₂SnF₉·0.9HF, O₂GeF₅·HF, and O₂[Hg(HF)]₄(SbF₆)₉ Compounds and Unit Cell Data for O₂GeF₅.

chemical formula	O2GeF5·HFa	O2Sn2F9·0.9HF	β-O2Sn2F9 (2-D)
Fw (g/mol)	219.60	460.39	440.42
crystal system	monoclinic	monoclinic	monoclinic
space group	I2/a	P21/c	P21/c
a (Å)	9.8444(8)	8.9497(5)	9.1318(9)
b (Å)	8.0274(6)	10.5235(5)	9.8027(5)
c (Å)	13.1030(12)	8.7920(4)	8.7741(6)
α (deg)	90	90	90
β (deg)	110.774(10)	94.401(5)	105.334(8)
γ (deg)	90	90	90
V (Å3)	968.14(15)	825.61(7)	757.46(10)
Z	8	2	4
T (K)	150	150	150
R1b	0.0278	0.0351	0.0569
wR2c	0.0722	0.0944	0.158

chemical formula	α-O2Sn2F9 (1-D)	O2[Hg(HF)]4(SbF6)9
Fw (g/mol)	440.42	3036.14
crystal system	orthorhombic	monoclinic
space group	Immm	C2/c
a (Å)	4.0473(3)	21.0387(6)
b (Å)	8.0199(4) Å	10.2412(3)
c (Å)	11.4491(8)	21.1577(6)
α (deg)	90	90
β (deg)	90	99.489(2)
γ (deg)	90	90
V (Å3)	371.63(4)	4496.3(2)
Z	2	4
T (K)	200d	150
R1b	0.0152	0.0364
wR2c	0.0362	0.0860

^aFor nonsolvated O₂GeF₅, only the unit cell was determined: monoclinic, P2₁/n, a = 6.070(2) Å, b = 4.993(1) Å, c = 13.197(4) Å, β = 96.93(3)°, V = 397.2 ų, Z = 4, T = 150 K.

^bR₁ = Σ||F₀| – |F_c||/Σ|F₀| for I > 2σ(I).

^cwR₂ = [Σ[w(F₀² – F_c²)²]/Σw(F₀²)²]^1/2.

^dCrystal structure determined at 296 K is the same as at 200 K.

Crystal Structures Containing Polymeric [GeF₅]⁻ Anions

Besides the well-known octahedral [GeF₆]^2– anion, only two other examples of fluoridogermanate(IV) anions have been described. The first is the polymeric chainlike ([GeF₅]⁻)_∞⁵⁷ anion and the second is the [Ge₃F₁₆]^4– oligomer.⁵⁸ Both are built from GeF₆ octahedra which share common vertices.

O₂GeF₅·HF

Low-temperature crystallization (Table 1) of the product of the reaction between GeF₄ and a UV-irradiated F₂/O₂ mixture in aHF resulted in the single crystals of O₂GeF₅·HF (Table 2). The crystal structure consists of infinite polymeric ([GeF₅]⁻)_∞ anions, which appear as zigzag single chains of GeF₆ octahedra (Figure 1) linked by cis-vertices and O₂⁺ cations and HF molecules located between the chains (Figure 2).

Figure 1.

Geometry of ([GeF₅]⁻)_∞ anions in O₂GeF₅·HF and hydrogen bonding between HF molecules and the polymeric anions. Thermal ellipsoids are drawn at the 50% probability level.

Figure 2.

Unit cell and packing of anions, cations, and HF molecules in the crystal structure of O₂GeF₅·HF.

The crystal structure of ClO₂GeF₅ also contains infinite polymeric ([GeF₅]⁻)_∞ anions appearing as zigzag single chains of GeF₆ octahedra linked by cis-vertices.⁵⁷ However, despite the same motif in the GeF₅ chain, the conformations of ([GeF₅]⁻)_∞ anions in ClO₂GeF₅ and O₂GeF₅·HF are different (Figure S12, see the Supporting Information). The geometry of the ([GeF₅]⁻)_∞ chains in ClO₂GeF₅ is similar to that observed for ([MnF₅]⁻)_∞ in XeF₅MnF₅⁵⁹ and ([TiF₅]⁻)_∞ in [C(NH₂)₃]₄[H₃O]₄[Ti₄F₂₀][TiF₅]₄,⁶⁰ whereas the geometry of the ([GeF₅]⁻)_∞ anion in O₂GeF₅·HF is closer to that of ([TiF₅]⁻)_∞ determined in A[TiF₅], A[TiF₅]·HF (A = Na, K, Rb, Cs)⁶¹ and [enH₂]_0.5[TiF₅] (en = ethylenediamine).⁶² In the crystal structure of O₂GeF₅·HF, there is one crystallographically unique germanium atom coordinated by six crystallographically independent fluorine atoms, resulting in slightly distorted GeF₆ octahedra. The Ge–F_t bond lengths between germanium atoms (Ge) and terminal fluorine atoms (F_t) range from 1.729(2) Å to 1.7545(19) Å and are shorter than the bonds between Ge and the bridging fluorine atoms (F_b): 1.8817(3) Å for Ge–F6 and 1.8934(9) Å for Ge–F7. They are comparable to those observed in ClO₂GeF₅ and XeF₅GeF₅ [Ge–F_t = 1.728(3)–1.75(2) Å and Ge–F_b = 1.887(1)–1.890(1) Å]. The observed Ge–F6–Ge and Ge–F7–Ge angles are 180.0° and 140.04(13)°, respectively. Thus, the zigzag chains of ([GeF₅]⁻)_∞ anions in O₂GeF₅·HF are oriented along the a-axis (Figure 1). Each GeF₆ octahedron of the ([GeF₅]⁻)_∞ chain has one interaction with one HF molecule by means of a hydrogen bond, where the (Ge−)F4···(H−)F1 distance is 2.511 Å.

O₂GeF₅

The reaction between GeF₄ and F₂/O₂ exposed to UV-light in the absence of solvent (Table 1) resulted in crystalline O₂GeF₅ (Figure S4, see the Supporting Information). Since numerous repeated attempts to obtain good quality X-ray diffraction data were unsuccessful, only the unit cell is reported (Table 2). Preliminary results show that the geometry of the anion is the same as that in the HF-solvated form, O₂GeF₅·HF, i.e., both compounds consist of polymeric ([GeF₅]⁻)_∞ chainlike anions of the same geometry. It can be concluded that O₂GeF₅·HF prepared at low temperature releases HF at elevated temperature to form O₂GeF₅. This is in accordance with the formula unit volumes (V_F.U.) of both compounds: O₂GeF₅; V_F.U = 99.3 ų and O₂GeF₅·HF; V_F.U = 121.0 ų. The difference of 21.7 ų can be attributed to the presence of HF in the latter.

Crystal Structures Containing ([Sn₂F₉]⁻)_∞ Double Chainlike and Layerlike ([Sn₂F₉]⁻)_∞ Anions

Raman spectroscopy indicates that the chemical reactions of SnO₂ or a SnO₂/SnF₄ mixture with a UV-irradiated F₂ or O₂/F₂ mixture in aHF always resulted in two or three phases (Figure S7, see the Supporting Information), which was confirmed by their single-crystal X-ray structures. The crystal structures of three unique O₂⁺ salts, all containing polymeric ([Sn₂F₉]⁻)_∞ anions, were determined. Two of them have the same empirical chemical formula, O₂SnF₉. The anion in the first salt has a chainlike structure, and the second salt has a layerlike structure. To distinguish them, the former is designated as 1-D (one-dimensional) and the latter as 2-D (two-dimensional). The third phase is the HF solvated form of 2-D O₂Sn₂F₉ (i.e., 2-D O₂Sn₂F₉·0.9HF). Bearing in mind that the Rb analogue of NaTi₂F₉ exists as the HF solvated form RbTi₂F₉·HF,⁶¹ the existence of a double chain-like 1-D O₂Sn₂F₉·nHF structure cannot be ruled out.

The layered, polymeric ([Sn₅F₂₄]^4–)_∞ anion determined in [XeF₅]₄[Sn₅F₂₄] is the only example of a structurally characterized Sn(IV) fluoride compound that so far does not consist of only [SnF₆]^2– anions.⁶³ Characterizations of other fluoridostannate(IV) anions have been limited to vibrational and NMR spectroscopy (tetrameric [Sn₄F₂₀]^4– and dimeric [Sn₂F₁₀]^2– oligomers).^64,65 Compounds with empirical composition [N₂F][Sn₂F₉] and [N₂F₃][SnF₅] have also been reported.^66,67 The former most likely does not have a monomeric structure but is more likely present as an oligomer [Sn₄F₁₈]^2– or polymeric infinite, double ([Sn₂F₉]⁻)_∞ chain, while the latter most probably has chainlike geometry similar to the ([TiF₅]⁻)_∞ anions observed in titanium-based compounds.⁶¹ With 18 different structurally characterized oligomeric and polymeric fluoridotitanate(IV) anions [Ti_nF_4n+x]^x− (n, x ≥ 1), the chemistry of TiF₄ has been much more extensively investigated⁶⁰⁻⁶² than those of GeF₄ and SnF₄.

α-O₂Sn₂F₉ (1-D)

The polymeric ([Sn₂F₉]⁻)_∞ anions in α-O₂Sn₂F₉ (1-D) appear as two parallel, infinite zigzag chains comprised of SnF₆ units, where each SnF₆ unit of one chain is connected to a SnF₆ unit of the second chain through a shared fluorine vertex (Figure 3).

Figure 3.

([Sn₂F₉]⁻)_∞ anion in the crystal structure of α-O₂[Sn₂F₉] (1-D). Thermal ellipsoids are drawn at the 50% probability level.

The geometries of such polymeric ([M₂F₉]⁻)_∞ anions have been previously observed in various [Ti₂F₉]⁻ salts.^60,61 However, there is one significant difference. In those compounds, the Ti–F_b–Ti angles within the individual chains, which form double chainlike ([Ti₂F₉]⁻)_∞ anions, are in the 150–160° range, while the Ti–F_b–Ti angles where the titanium atoms belong to two neighboring chains are in the 140–164° range. The corresponding Sn–F_b–Sn angles in ([Sn₂F₉]⁻)_∞ are more open. The Sn1–F3–Sn1 angles within the individual chains are equal to 170.7(2)°), and the angles, where the Sn atoms belong to two neighboring chains, are linear (Sn1–F4–Sn1 = 180°).

The Sn atom is coordinated by six fluorine atoms. The three Sn–F_b bond lengths between tin and the bridging fluorine atoms are elongated (2 × Sn1–F3 = 2.0303(3) Å, Sn1–F4 = 2.0374(4) Å) in comparison with the three Sn–F_t bonds between tin and the terminal fluorine atoms (2 × Sn1–F1 = 1.898(2) Å, Sn1–F4 = 1.909(4) Å).

The negative charge of ([Sn₂F₉]⁻)_∞ anions is compensated by partially disordered O₂⁺ cations located between the chains (Figure 4).

Figure 4.

Unit cell and packing of anions, cations, and HF molecules in the crystal structure of α-O₂Sn₂F₉ (1-D).

O₂[Sn₂F₉]·0.9HF

Dioxygenyl nonafluoridodistannate(IV) also crystallized from saturated HF solution as the solvate, O₂[Sn₂F₉]·0.9HF. The single-crystal structure determination of O₂[Sn₂F₉]·0.9HF reveals that its structure is different from that of O₂[Sn₂F₉] (1-D). The anions resemble that determined in [XeF₅]₄[Sn₅F₂₄].⁶³ In both compounds (1) the anions consist of two-dimensional (2-D) grids, i.e., ([Sn₅F₂₄]^4–)_∞ and ([Sn₂F₉]⁻)_∞, respectively (Figure S13, see Supporting Information), and the [XeF₅]⁺ or O₂⁺ cations and HF molecules, respectively, are located between the grids (Figure 5). (2) Both types of 2-D grids have wavelike conformations (Figure S13, see Supporting Information), (3) Both the ([Sn₅F₂₄]^4–)_∞ and ([Sn₂F₉]⁻)_∞) layers contain six- and seven-coordinated Sn(IV) interconnected by bridging fluorine atoms, and (4) SnF₇ polyhedra in both cases share one edge forming dimer (Figure 6 and Figure S14, see Supporting Information).

Figure 5.

Two-dimensional ([Sn₂F₉]⁻)_∞ grids with a wavelike conformation with the O₂⁺ cations and HF molecules located between them in the crystal structure of O₂[Sn₂F₉]·0.9HF.

Figure 6.

([Sn₂F₉]⁻)_∞) layer in the crystal structure of O₂[Sn₂F₉]·0.9HF contains both six- and seven-coordinated Sn(IV) interconnected by bridging fluorine atoms (view perpendicular to the layer, along the a-axis).

The Sn–F bond lengths in O₂Sn₂F₉·0.9HF (2-D), α-O₂Sn₂F₉ (1-D), and [XeF₅]₄[Sn₅F₂₄]⁶³ can be divided into several groups (Table 3, Figure 7). The Sn–F_b(−Sn) bonds (F_b = fluorine atoms that bridge two Sn atoms) are longer in seven-coordinated (2.057(4)–2.1120(5) Å) than in six-coordinated Sn(IV) (1.992(6)–2.0374(4) Å). The Sn–F_b(···Xe) bonds, where F is involved in secondary bonding interactions with [XeF₅]⁺ cations or in hydrogen bonding with HF molecules, are shorter (1.919(5)–1.963(6) Å) but longer than the Sn–F_t bonds (F_t = terminal fluorine atoms) of the seven- (1.879(6)–1.883(6) Å) and six-coordinated Sn atoms (1.898(2)–1.909(4) Å).

Table 3. Geometrical Parameters of Layerlike (2-D) ([Sn₂F₉]⁻)_∞ and the Chainlike (1-D) Anions in the Crystal Structures of O₂[Sn₂F₉]·0.9HF (2-D) and O₂[Sn₂F₉] (1-D) and Literature Data for ([Sn₅F₂₄]^4–)_∞ Observed in [XeF₅]₄[Sn₅F₂₄].

C.N.	bond/Å	[XeF5]4[Sn5F24]a	O2Sn2F9·0.9HF (2-D)	α-O2Sn2F9 (1-D)
7	Sn–Ft	1.879(6)/1.883(6)	1.880(4)/1.887(4)
6	Sn–Ft		1.907(4)/1.909(4)	1.898(2)–1.909(4)
6	Sn–Fb···(H–F)		1.933(4)
6	Sn–Fb···(XeF5)	1.919(5)–1.963(6)
6	Sn–Fb(−Sn)	1.992(6)/2.002(5)	1.999(4)–2.010(4)	2.0303(3)–2.0374(4)
7	Sn–Fb(−Sn)	2.068(6)–2.120(5)	2.057(4)–2.095(4)

^aReference (63).

Figure 7.

Coordination of two crystallographically unique Sn(IV) atoms and the secondary bonding interactions between SnF₆ octahedra and HF molecules in the crystal structure of O₂Sn₂F₉·0.9HF (2-D). Thermal ellipsoids are drawn at the 50% probability level. Symmetry operations are (i) 2 – x, −1/2 + y, 3/2 – z; (ii) 2 – x, −y, 1 – z; (iii) x, 1/2 – y, 1/2 + z; and (iv) x, 1/2 – y, −1/2 + z.

HF molecules are bound to 2-D grids through F–H···F hydrogen bonds (H···F 1.84 Å, F···F 2.552(7) Å, F···H–F angle 140°). The position of the HF molecule is partially filled, which is likely due to the relative weakness of the above-mentioned hydrogen bonding.

β-O₂[Sn₂F₉] (2-D)

The third product that resulted from the reaction between SnO₂ or SnO₂/SnF₄ mixture and a UV irradiated F₂ or O₂/F₂ mixture in aHF is HF-free O₂[Sn₂F₉] which is denoted by β-O₂[Sn₂F₉] (2-D). Unfortunately, the same problems as those encountered in the case of unsolvated O₂GeF₅ were observed, i.e., attempts to obtain good quality X-ray diffraction data failed (Table 2). The geometry of the anion is the same as that of solvated O₂Sn₂F₉·0.9HF (2-D), i.e., a layerlike ([Sn₂F₉]⁻)_∞) anion that is present in both compounds. The formula unit volume of O₂Sn₂F₉ (1-D) is smaller than that of O₂Sn₂F₉ (2-D). For the former, V_F.U. = 185.82 ų at 200 K, and for the latter, V_F.U. = 189.37 ų at 150 K (Table 2). Because of better packing, O₂Sn₂F₉ (1-D) should be a more thermodynamically stable product.

Crystal Structure of O₂[Hg(HF)]₄(SbF₆)₉

The crystal structure of O₂[Hg(HF)]₄(SbF₆)₉ is isotypic with that of H₃O[Cd(HF)]₄(SbF₆)₉.⁶⁸ It exhibits a complex three-dimensional structure consisting of two crystallographically unique Hg atoms, five crystallographically independent SbF₆ groups, and one HF molecule bound to Hg atoms through its F atom. They form a complex framework with O₂⁺ cations located inside the voids (Figure 8).

Figure 8.

Unit cell and packing of anions, cations, and HF molecules in the crystal structure of O₂[Hg(HF)]₄(SbF₆)₉.

The Hg1 and Hg2 atoms both possess a square antiprismatic spheres comprised of seven fluorine atoms belonging to seven SbF₆ units and the F atom of the HF molecule. The Hg1–F bond lengths lie in a narrow range, 2.386(5)–2.370(5) Å. The coordination sphere of Hg2 is noticeably distorted; its shape deviates significantly from an ideal square antiprism, and the Hg2–F distances are 2.367(5)–2.451(5) Å.

Four SbF₆^– anions play a role in μ₃-bridging, being bound to three Hg cations in a mer-arrangement, and a SbF₆^– moiety built up around the Sb5 atom displays a μ₄-bridge (Figure 9). The lengths of the terminal Sb–F bonds of the Sb1 to Sb4 polyhedra vary from 1.838(5) to 1.859(6) Å. Notable elongations of Sb3–F33 (1.862(5) Å) and especially Sb4–F43 and Sb1–F13 bonds to 1.868(5) and 1.870(5) Å, respectively, may be attributed to the influence of F–H···F(−SbF₅) bond formation (F33···H2, 2.13 Å; F43···H1, 1.99 Å; F13···H2, 2.04 Å). The lengths of bridging Sb–F bonds are 1.891(5)–1.912(5) Å. In the case of the Sb6 coordinating sphere, the two terminal Sb–F bonds, 1.840(8) and 1.862(7) Å, and the bridging Sb–F contacts vary from 1.881(5) to 1.895(5) Å. Each of two HF molecules are bound to the corresponding metal center with Hg–F distances of 2.367(5) and 2.386(5) Å forming rather strong F–H···F hydrogen bonds as noted above. The large increased thermal ellipsoids of oxygen atoms and the short O···O distance of 0.89(2) Å are a consequence of significant orientational disorder of the O₂⁺ cation.

Figure 9.

Part of the crystal structure of O₂[Hg(HF)]₄(SbF₆)₉ showing the environments of both Hg centers and the O₂⁺ cation. Fluorine atoms around Sb (with the exception of Sb1) atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Symmetry operations are (i) −x, 2 – y, 1 – z; (ii) 1 – x, 1 – y, 1 – z; (iii) x, 1 – y, 1/2 + z; (iv) x, −1 + y, z; (v) x, 1 – y, −1/2 + z; (vi) 1/2 – x, 1/2 – y, 1 – z; and (vii) 1/2 – x, 1/2 + y, 1/2 – z.

O₂⁺ Bond Lengths

A list of the O–O bond lengths determined in various O₂⁺ salts (including this work) is given in Table 4.

Table 4. O–O Distances (Å) in O₂⁺ Salts Determined by Single Crystal X-Ray Diffraction Data (O₂PtF₆ Was Studied Also Using Neutron-Diffraction Data from a Polycrystalline Sample).

O2+ salt	O–O (Å)	T/K	ref
O2[Hg(HF)]4(SbF6)9	0.89(2)	150	this work
O2SbF6	0.95	RT	(22)
(O2)2Ti7F30	0.96	153	(29)
O2GeF5·HF	1.013(4)	150	this work
O2H3Pd2F12	1.014(4)	140	(21)
O2Ni(AsF6)3	1.018(12)	173	(20)
O2Sn2F9·0.9HF	1.046(9)	150	this work
α-O2Sn2F9 (1-D)	1.062(14)	200	this work
O2Mn2F9	1.10	123	(30)
	0.96	293	(30)
O2RhF6a	1.1107(16)	133	(25)
β-O2AuF6	0.97	RT	(22)
α-O2AuF6a	1.079(27)	104	(23)
	1.068(30)	151	(24)
	1.1091(28)	133	(25)
O2RuF6	1.00	RT	(22)
	1.125(17)	146	(26)
	1.12(4)	298	(26)
O2PtF6	0.91(3)/1.21(17)/1.40b	RT	(27)
	0.96	RT	(22)
free O2+	1.1227		(69)

^aRare examples of O₂⁺ salts with ordered O₂⁺ cations.

^bFrom a neutron diffraction study. Various models were tested in an attempt to interpret the experimental data resulting in O–O distances ranging from 0.91 to 1.4 Å. A definitive value for the O–O bond length was not determined, but according to the authors, the model yielding a value of 1.21(17) Å represents the most satisfactory value for the structure of O₂PtF₆.

The reported O–O bond lengths of O₂⁺ span the absurdly short value of 0.89(2) Å to values close to that observed for the gas-phase O₂⁺ cation (1.1227 Å). Their comparison can be difficult due to the large uncertainty of their values. The determination of O–O bond lengths of O₂⁺ is often problematic because of the partial or complete disorder of the O₂⁺ cation in the crystal structures of O₂⁺ salts. For example, the first reported value for O–O bond length in O₂RuF₆ was 1.00 Å (at RT).²² A 3-fold disordering of O₂⁺ yielded a more realistic value of 1.12(4) Å (at 298 K).²⁶ Closer inspection of thermal ellipsoids of oxygen atoms in O₂[Hg(HF)]₄(SbF₆)₉ (Figure 9) reveals unusual enlarged and elongated thermal ellipsoids consistent with oxygen atoms that exhibit static or dynamic disorders. A similar situation occurs in the cases of O₂GeF₅·HF, α-O₂Sn₂F₉ (1-D), and O₂Sn₂F₉·0.9HF. Applying of libration corrections did not result in significant elongation of O–O bonds. More fruitful was an attempt to split oxygen atom positions in α-O₂Sn₂F₉ (1-D) salt. The resulting O–O distance appears to be more adequate, i.e., 1.06(1) Å instead of 0.97(1) Å, for a model without O₂⁺ disordering.

Conclusions

Photochemical reactions of UV-irradiated O₂/F₂ mixtures with solid, liquid, or gaseous fluorides, and oxides with UV-irradiated F₂ (or O₂/F₂ mixtures) in anhydrous HF are a convenient way to synthesize O₂⁺ salts (Table 5).

Table 5. List of Reported of O₂⁺ Salts (Including This Work) Together with ν(O₂⁺) Values Recorded by Raman Spectroscopy.

O2+ salt	ν(O2+)a	crystal structure	ref
molecular O2	1580		(70)
(O2)2NiF6	1801		(37)
(O2)2MnF6	1805		(37)
O2PdF5	1820		(36), this work
O2RhF6	1825	y	(23, 25, 26, 47)
β-O2AuF6	1835b	y	(24, 47), this work
α-O2AuF6	1838c	y	(24)
O2Mn2F9	1838	y	(30)
O2RuF6	1838	y	(22, 26, 47)
O2PtF6	1838	y	(16, 17, 22, 27, 44, 47), this work
O2V2F11	1839		(71)
O2BiF6	1849		(43, 47)
O2GeF5	1849	yd	(35), this work
α-O2Sn2F9 (1-D)	1849	y	this work
O2Bi2F11	1853		(43)
O2NbF6	1853		(43)
(O2)2Ti7F30	1857	y	(29), This work
O2AsF6	1858		(41, 42, 47, 55), this work
O2Nb2F11	1858		(43, 47)
O2Ta2F11	1858		(43, 47)
O2BF4	1860	y	(28), this work
O2SbF6	1861	y	(22, 45, 47), this work
O2[Hg(HF)]4(SbF6)9	1861	y	this work
(O2)2Hg2F(SbF6)5	1863	y	(53)
O2Sb2F11	1864		(45, 47)
O2Ni(AsF6)3	1866	y	(20)
gaseous O2+	1876.4		(69)
O2Pt2F11		yd	(48)
[O2][H3Pd2F12]		y	(21)
O2AgF4		yd	(33)
O2GeF5·HF		y	this work

^aThe values of O₂⁺ stretch are strongly dependent on the nature of counteranions. For more detailed discussion about this topic, see the literature.^24,72

^bRecorded at 25 °C

^cRecorded at −163 °C.

^dComplete structure data are not available.

In addition to those given in Table 5, a few others have been mentioned in the literature. The addition of a solution of highly soluble salts A₂PdF₆ (A = K, Cs) in aHF to a solutions of O₂AsF₆ in aHF at −30 °C yield precipitates of AAsF₆ and deep orange solutions presumed to contain (O₂)₂PdF₆.³⁶ Attempts to isolate these salts by removal of aHF at −60 °C always resulted in the loss of O₂ and F₂ and recovery of O₂PdF₅.³⁶ However, further crystallizations at T < −70 °C resulted in the growth of single crystals of [O₂][H₃Pd₂F₁₂].²¹ The (O₂)₂SnF₆, O₂MoF₇ and O₂WF₇ salts have been reported for the reactions between O₂F₂ and SnF₄ and WF₆ or MoF₆, respectively.³⁸ However, these reactions are of low yield and poor reproducibility. The compound, O₂PF₆, slowly decomposes at −80 °C and rapidly at room temperature, giving O₂, F₂ and PF₅.^42,73 The existence of O₂VF₆, O₂CrF₆, O₂Ru₂F₁₁, and O₂M₃F₁₆ (M = Sb, Nb, Ta) still await confirmation.^46,71,74 Reported formulation, O₂PdF₆,⁷⁵ is most probably O₂PdF₅,³⁶ whereas O₂[CrF₄Sb₂F₁₁],⁷⁶ which was claimed to be prepared by oxidation of O₂ with CrF₅·2SbF₅, is in reality a mixture of O₂Sb₂F₁₁ and CrF₄.⁷⁷

Determination of the single-crystal X-ray structure of O₂GeF₅·HF showed that its structure consists of infinite polymeric ([GeF₅]⁻)_∞ anions, which appear as zigzag single chains of GeF₆ octahedra linked by cis-vertices and O₂⁺ cations and HF molecules located between the chains. The ([GeF₅]⁻)_∞ anion of O₂GeF₅ appears to have the same structural motif as that of O₂GeF₅·HF.

Three different O₂⁺ salts, all containing polymeric ([Sn₂F₉]⁻)_∞ anions, were isolated and their structured determined. Two of them have the same empirical chemical formula as O₂Sn₂F₉. The anion in α-O₂Sn₂F₉ (1-D) has a chainlike structure, and the anion in β-O₂Sn₂F₉ (2-D) has a layerlike structure. The third phase is the HF solvated form of 2-D O₂Sn₂F₉ (i.e., O₂Sn₂F₉·0.9HF). Besides the layered polymeric ([Sn₅F₂₄]^4–)_∞ anion determined in [XeF₅]₄[Sn₅F₂₄],⁶³ these salts provide new examples of structurally characterized Sn(IV) fluoride compounds which do not only consist of [SnF₆]^2– anions.

The complex O₂⁺ salt O₂[Hg(HF)]₄[SbF₆]₉ was prepared by reaction between O₂SbF₆, HgF₂, and SbF₅ in anhydrous aHF. Its crystal structure is isotypic to that of (H₃O)[Cd(HF)]₄(SbF₆)₉.⁶⁸

Experimental Section

Caution! Anhydrous HF and some fluorides are highly toxic and must be handled in a well-ventilated hood, and protective clothing must be worn at all the times.

Materials and Methods

Reagents

Commercially available reagents BF₃ (Union Carbide Austria GmbH, 99.5%), FeF₃ (Alfa Aesar, 97% min), CoF₂ (Johnson Matthey GmbH, 99%), TiO₂ (Koch-Light Laboratories Ltd., 99.5%), SnO₂ (E. Merck AG, Darmstadt, pure), PbO₂ (Riedel de Haën), GeF₄ (Cerac, Incorporated, 99.99%), NiF₂ (Alfa Products, 99.5%), MnF₂ (Alfa Aesar, 99%), SnF₄ (Alfa Aesar, 99%), SbF₃ (Merck KGaA, ≥99%), Pt (Aldrich, ≥99.9%), PtO₂ (Aldrich), SeO₂ (Fluka AG, Buchs SG, >98%), WO₃ (Merck), MoO₃ (Merck, 99.5%), WF₆ (ABCR, 99%), SbCl₅ (Merck, >99%), TiCl₄ (Acros Organics, 99.9%), NbCl₅ (Alfa Aesar, 99.95%), HCl, and Cl₂ were used as supplied. AgF₂, AuF₃, and Pd₂F₆ were synthesized by the reaction of AgNO₃ (Fisher Chemical), AuCl₃ (Alfa Aesar, 99.99%), and Pd sponge (Aldrich 99.9%), respectively, with elemental fluorine F₂ (Solvay Fluor and Derivate GmbH, 99.98%) in aHF (Linde AG, Pullach, Germany, 99.995%) at ambient temperature.³¹ Arsenic pentafluoride was prepared as described previously,⁷⁸ and IF₅ was from our stock. HgF₂ was obtained by high temperature (230 °C) static fluorination of HgCl₂ (Alfa Aessar, 99.5%) in a 100 mL nickel autoclave.

Synthetic Apparatus

All manipulations were carried out under anhydrous conditions. Nonvolatile materials were handled in a M. Braun glovebox in an argon atmosphere, where the quantity of water did not exceed 0.5 ppm. Gaseous F₂, O₂, and AsF₅ and volatile compounds, such as aHF and WF₆, were handled on a vacuum line constructed from nickel and PTFE (polytetrafluoroethylene).

Vessels used for syntheses and single-crystal growth were manufactured from tetrafluoroethylene-hexafluoropropylene block-copolymer (FEP; Polytetra GmbH, Germany) tubes. The reaction vessel was comprised of a tube (i.d. 16 mm, o.d. 19 mm) that was heat-sealed on one end and equipped with a PTFE valve on the other flared end. The crystallization vessel consisted of two FEP tubes: one 16 mm i.d. × 19 mm o.d. and the other 4 mm i.d. × 6 mm o.d. Each tube was heat-sealed on one end and attached via linear PTFE connectors to a connecting PTFE T-part at 90°. The PTFE valve was attached to the T-part at 180° to the 19 mm o.d. tube. All PTFE portions of valve were enclosed in brass with threads that prevented deformation of the PTFE portions of the valve and simplified their connection to reaction vessels and to the vacuum system. Magnetic stirring bars, clad in PTFE, were placed inside the reaction vessels. The temperature gradient between the two arms of the crystallization vessels was maintained by cooling a wider arm of a vessel in Huber Ministat 230 (to −33 °C) and Thermo Fisher Scientific EK 90 (to −60 °C) cryostats.

Prior to use, all reaction and crystallization vessels were dried under dynamic vacuum and passivated with elemental fluorine F₂ (Solvay Fluor and Derivate GmbH, 99.98%) at 1 bar for 2 h. Anhydrous HF (Linde AG, 99.995%) was treated with K₂NiF₆ (Advance Research Chemicals Inc., 99.9%) for several hours before use and was usually kept in FEP vessels above K₂NiF₆.

Synthesis and Crystal Growth

Various amounts (50–200 mg) of solid starting reagents were loaded into reaction vessels inside a drybox (Table S1 in the Supporting Information). Gaseous and liquid reagents were added on a vacuum line. Solvent (HF, 5–10 mL) was condensed onto the reactant at 77 K, and the reaction mixture was warmed to ambient temperature. Fluorine was slowly added to the reaction vessel at ambient temperature until a pressure of 6 bar was attained. A medium-pressure mercury lamp (Hg arc lamp, 450 W, Ace Glass, USA) was used as the UV source.³¹ The reaction mixture was allowed to stir for 1–5 days at ambient temperature. All volatiles were slowly pumped off at ambient temperature. After characterization, the powdered product was transferred to a crystallization vessel where aHF (6–10 mL) was condensed onto the product at 77 K. The solvent and product were warmed to ambient temperature and the resulting clear solution was decanted into the 6 mm o.d. side arm. Evaporation of the solvent from this side arm was carried out by maintaining a temperature gradient of ∼10–20 °C between both tubes for several weeks. Slow distillation of aHF from the 6 mm o.d. tube into the 19 mm o.d. tube resulted in crystal growth inside the 6 mm o.d. tube. Several solutions of dissolved products were allowed to crystallize without prior isolation and characterization.

Crystals were treated in different ways. Some crystals were immersed in perfluorodecalin (melting point 263 K) inside a drybox, selected under a microscope, and mounted on the goniometer head of the diffractometer in a cold nitrogen stream. Others were sealed in quartz capillaries used for the structure determination at room temperature and recording of Raman spectra at several random positions. A special method was applied in order to isolate crystals of O₂GeF₅·HF that are not stable at ambient temperature. For this, a small portion (1–2 mL) of cold perfluorinated oil (perfluorodecaline C₁₀F₁₈) was injected inside the narrower FEP tube to cover the crystals. After that, crystals covered with cold oil were selected under a microscope and mounted on the goniometer head of the diffractometer in a cold nitrogen stream.

Characterization Methods

Raman Spectroscopy

Raman spectra with a resolution of 0.5 cm^–1 were recorded at room temperature on a Horiba Jobin Yvon LabRam-HR spectrometer equipped with an Olympus BXFM-ILHS microscope. Samples were excited by the 632.8 nm emission line of a He–Ne laser with a regulated power in the range 20–0.0020 mW, which gave 17–0.0017 mW focused on a 1 μm spot through a 50× microscope objective on the top surface of the sample. Single crystals or powdered material were mounted in the glovebox in previously vacuum-dried quartz capillaries, which were initially sealed with Halocarbon 25-5S grease (Halocarbon Corp.) inside the glovebox and later heat-sealed in an oxygen–hydrogen flame outside the glovebox.

Single Crystal X-ray Diffraction Analysis

Single-crystal X-ray data for O₂Sn₂F₉ (1-D and 2-D), O₂Sn₂F₉·0.9HF, O₂GeF₅·HF, O₂GeF₅, and O₂[Hg(HF)]₄(SbF₆)₉ were collected on a Gemini A diffractometer equipped with an Atlas CCD detector, using graphite monochromated MoKα radiation. The data were treated using the CrysAlisPro software suite program package.⁷⁹ Analytical absorption corrections were applied to all data sets. The structure of O₂Sn₂F₉ (1-D) was solved using the SHELXS program.⁸⁰ All other structures were solved using the dual-space algorithm of the SHELXT⁸¹ program implemented in the Olex crystallographic software.⁸² Structure refinement was performed with SHELXL-2014 software.⁸³ The figures were prepared using DIAMOND 4.6 software.⁸⁴ Hydrogen atoms in the structures of O₂Sn₂F₉·0.9HF, O₂GeF₅·HF, and O₂[Hg(HF)]₄(SbF₆)₉ were placed on ideal positions and refined as the riding atoms with relative isotropic displacement parameters. The common occupancy of atoms belonging to the HF molecule in the O₂Sn₂F₉·0.9HF structure was refined using a free variable.

Crystals of O₂GeF₅ and O₂Sn₂F₉ (2-D) compounds were of extremely poor quality. In the case of O₂Sn₂F₉ (2-D), the crystal structure was completely solved and refined to a reasonable R-factor value. However, the structure suffers from residual electron densities having peaks that are too high. Only the structural motif was identified in the case of O₂GeF₅ salt with a very high R-value (∼20%) for the completed model.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b03518.

• Raman spectra of the products obtained by photochemical reactions of UV-irradiated F₂ (or O₂/F₂ mixture) with solid, liquid, or gaseous fluorides or oxides in anhydrous HF; photos of the yellow solids formed after SbCl₅/Cl₂/O₂ and TiCl₄/Cl₂/O₂/HCl mixtures were irradiated by UV-light; geometries of the ([GeF₅]⁻)_∞ anions determined in the crystal structures of O₂GeF₅·HF and [ClO₂][GeF₅]; two-dimensional ([Sn₂F₉]⁻)_∞ and ([Sn₅F₂₄]^4–)_∞ grids with a wavelike conformation found in O₂[Sn₂F₉]·0.9HF and [XeF₅]₄[Sn₅F₂₄] (PDF)

Accession Codes

CCDC 1964935–1964938 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

The authors declare no competing financial interest.