Synthesis and characterization of the first examples of perfluoroalkyl-substituted trialkyloxonium salts, [(CH3)(2)OCF3](+)[Sb2F11](-) and [(CH3)(2)OCF(CF3)(2)](+)[Sb2F11](-)

In the superacidic HF/SbF5 system, methyl trifluoromethyl ether forms at -7 8 degreesC the new tertiary oxonium salt [(CH3)(2)OCF3](+)[Sb2F11](-), whic h was characterized by Raman and multinuclear NMR spectroscopy and its crys tal structure. The same oxonium salt was also obtained by methylation of CH 3OCF3 with CH3F and SbF5 in HF solution at -30 to -10 degreesC. Replacement of one methyl group in the trimethyloxonium cation by the bulkier and more electronegative trifluoromethyl group increases the remaining O-CH3 bond l engths by 0.037(1) A and the sum of the C-O-C bond angles by about 4.5 degr ees. Methylation of CH3OCF(CF3)(2) with CH3F in HF/SbF5 solution at -30 deg reesC produces [(CH3)(2)OCF(CF3)(2)](+)[Sb2F11](-). The observed structure and vibrational and NMR spectra were confirmed by theoretical studies at th e B3LYP/6-311++G(2d,2p) and the MP2/6-311++G(2d,p) levels.