Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5]+ and [Xe2F11]+ Salts of the [CrVIOF5]−, [CrVOF5]2−, [CrV2O2F8]2−, and [CrIVF6]2− Anions
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abstract
AbstractMolten mixtures of XeF6 and CrVIOF4 react by means of F2 elimination to form [XeF5][Xe2F11][CrVOF5]⋅2 CrVIOF4, [XeF5]2[CrIVF6]⋅2 CrVIOF4, [Xe2F11]2[CrIVF6], and [XeF5]2[CrV2O2F8], whereas their reactions in anhydrous hydrogen fluoride (aHF) and CFCl3/aHF yield [XeF5]2[CrV2O2F8]⋅2 HF and [XeF5]2[CrV2O2F8]⋅2 XeOF4. Other than [Xe2F11][MVIOF5] and [XeF5][MVI2O2F9] (M=Mo or W), these salts are the only Group 6 oxyfluoro‐anions known to stabilize noble‐gas cations. Their reaction pathways involve redox transformations that give [XeF5]+ and/or [Xe2F11]+ salts of the known [CrVOF5]2− and [CrIVF6]2− anions, and the novel [CrV2O2F8]2− anion. A low‐temperature Raman spectroscopic study of an equimolar mixture of solid XeF6 and CrOF4 revealed that [Xe2F11][CrVIOF5] is formed as a reaction intermediate. The salts were structurally characterized by LT single‐crystal X‐ray diffraction and LT Raman spectroscopy, and provide the first structural characterizations of the [CrVOF5]2− and [CrV2O2F8]2− anions, where [CrV2O2F8]2− represents a new structural motif among the known oxyfluoro‐anions of Group 6. The X‐ray structures show that [XeF5]+ and [Xe2F11]+ form ion pairs with their respective anions by means of Xe‐ ‐ ‐F–Cr bridges. Quantum‐chemical calculations were carried out to obtain the energy‐minimized, gas‐phase geometries and the vibrational frequencies of the anions and their ion pairs and to aid in the assignments of their Raman spectra.
