Abstract
Molten mixtures of XeF6 and CrVI OF4 react by means of F2 elimination to form [XeF5 ][Xe2 F11 ][CrV OF5 ]⋅2 CrVI OF4 , [XeF5 ]2 [CrIV F6 ]⋅2 CrVI OF4 , [Xe2 F11 ]2 [CrIV F6 ], and [XeF5 ]2 [CrV 2 O2 F8 ], whereas their reactions in anhydrous hydrogen fluoride (aHF) and CFCl3 /aHF yield [XeF5 ]2 [CrV 2 O2 F8 ]⋅2 HF and [XeF5 ]2 [CrV 2 O2 F8 ]⋅2 XeOF4 . Other than [Xe2 F11 ][MVI OF5 ] and [XeF5 ][MVI 2 O2 F9 ] (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 [Xe2 F11 ]+ salts of the known [CrV OF5 ]2- and [CrIV F6 ]2- anions, and the novel [CrV 2 O2 F8 ]2- anion. A low-temperature Raman spectroscopic study of an equimolar mixture of solid XeF6 and CrOF4 revealed that [Xe2 F11 ][CrVI OF5 ] 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 [CrV OF5 ]2- and [CrV 2 O2 F8 ]2- anions, where [CrV 2 O2 F8 ]2- represents a new structural motif among the known oxyfluoro-anions of Group 6. The X-ray structures show that [XeF5 ]+ and [Xe2 F11 ]+ 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.
Published Version
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