Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5]+ and [Xe2F11]+ Salts of the [Cr(VI)OF5]–, [Cr(IV)F6]2–, [Cr(V)OF5]2–, and [Cr(V)2O2F8]2– Anions

Molten mixtures of XeF₆ and Cr^VIOF₄ in 1:1 and 1:2 molar ratios undergo reduction to Cr(V) and Cr(IV) by means of F₂ elimination to form [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄ and [XeF₅]₂[Cr^IVF₆]∙2Cr^VIOF₄, respectively, as shown by low-temperature (LT) single-crystal X-ray diffraction (SCXRD). A LT Raman spectroscopic study of an equimolar mixture of solid XeF₆ and CrOF₄ and its melt showed that [Cr^VIOF₅]^– is formed as an intermediate. Reaction of [XeF₅]₂[Cr^IVF₆]∙2Cr^VIOF₄ with XeF₆ in a melt gave [Xe₂F₁₁]₂[Cr^IVF₆] and [XeF₅]₂[Cr^V₂O₂F₈]. Their LT crystal structures revealed that [XeF₅]⁺ and [Xe₂F₁₁]⁺ are coordinated to their respective [CrF₆]²⁻ and [Cr₂O₂F₈]²⁻ anions by means of Xe---F–Cr bridges to form infinite chain structures. The reactions of a 1:1 molar ratio of XeF₆ and CrOF₄ in anhydrous hydrogen fluoride (aHF) and in mixed CFCl₃/aHF solvents yielded [XeF₅]₂[Cr^V₂O₂F₈]∙2HF and a mixture of [XeF₅]₂[Cr^V₂O₂F₈]∙2HF and [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄, respectively. The SCXRD structures of the latter and aforementioned salts provide the first X-ray structures of [CrOF₅]^2– and [Cr₂O₂F₈]^2–. The [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄ and [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄ salts were also characterized by LT Raman spectroscopy. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and vibrational frequencies for [Cr^VIOF₅]^–, [XeF₅]₂[Cr^V₂O₂F₈]∙2XeOF₄, [Cr^V₂O₂F₈]^2–, [XeF₅][Xe₂F₁₁][Cr^VOF₅]∙2Cr^VIOF₄, [Cr^VOF₅]^2–, and to aid in the assignments of their vibrational frequencies.