Group 6 Oxyfluoro-Anion Salts of [XeF5 ]+ and [Xe2 F11 ]+ : Syntheses and Structures of [XeF5 ][M2 O2 F9 ] (M=Mo, W), [Xe2 F11 ][M'OF5 ] (M'=Cr, Mo, W), [XeF5 ][HF2 ]⋅CrOF4 , and [XeF5 ][WOF5 ]⋅XeOF4.

Abstract

The reactions of the fluoride-ion donor, XeF6 , with the fluoride-ion acceptors, M'OF4 (M'=Cr, Mo, W), yield [XeF5 ]+ and [Xe2 F11 ]+ salts of [M'OF5 ]- and [M2 O2 F9 ]- (M=Mo, W). Xenon hexafluoride and MOF4 react in anhydrous hydrogen fluoride (aHF) to give equilibrium mixtures of [Xe2 F11 ]+ , [XeF5 ]+ , [(HF)n F]- , [MOF5 ]- , and [M2 O2 F9 ]- from which the title salts were crystallized. The [XeF5 ][CrOF5 ] and [Xe2 F11 ][CrOF5 ] salts could not be formed from mixtures of CrOF4 and XeF6 in aHF at low temperature (LT) owing to the low fluoride-ion affinity of CrOF4 , but yielded [XeF5 ][HF2 ]⋅CrOF4 instead. In contrast, MoOF4 and WOF4 are sufficiently Lewis acidic to abstract F- ion from [(HF)n F]- in aHF to give the [MOF5 ]- and [M2 O2 F9 ]- salts of [XeF5 ]+ and [Xe2 F11 ]+ . To circumvent [(HF)n F]- formation, [Xe2 F11 ][CrOF5 ] was synthesized at LT in CF2 ClCF2 Cl solvent. The salts were characterized by LT Raman spectroscopy and LT single-crystal X-ray diffraction, which provided the first X-ray crystal structure of the [CrOF5 ]- anion and high-precision geometric parameters for [MOF5 ]- and [M2 O2 F9 ]- . Hydrolysis of [Xe2 F11 ][WOF5 ] by water contaminant in HF solvent yielded [XeF5 ][WOF5 ]⋅XeOF4 . Quantum-chemical calculations were carried out for M'OF4 , [M'OF5 ]- , [M'2 O2 F9 ]- , {[Xe2 F11 ][CrOF5 ]}2 , [Xe2 F11 ][MOF5 ], and {[XeF5 ][M2 O2 F9 ]}2 to obtain their gas-phase geometries and vibrational frequencies to aid in their vibrational mode assignments and to assess chemical bonding.