Protonated decafluorobenzophenone and the decafluorobenzophenone–arsenic pentafluoride adduct

The reaction of decafluorobenzophenone [perfluorobenzophenone, (C 6 F 5 ) 2 CO] with AsF 5 in anhydrous HF yields the protonated salt [bis(2,3,4,5,6-pentafluorophenyl)methylidene]oxidanium hexafluoridoarsenate, (C 6 F 5 ) 2 COH + [AsF 6 ] − , whereas its reaction with AsF 5 in SO 2 affords the Lewis acid–base adduct decafluorobenzophenone–arsenic pentafluoride, (C 6 F 5 ) 2 CO·AsF 5 . In both compounds, the decafluorobenzophenone moiety exhibits an elongated C=O bond [1.274 (2) and 1.2526 (15) Å in the salt and adduct, respectively]. The crystal structure of (C 6 F 5 ) 2 COH + [AsF 6 ] − features a short O—H...F hydrogen bond between the cation and the anion, and the crystal structure of (C 6 F 5 ) 2 CO·AsF 5 represents a rare example of a ketone coordinated to the strong Lewis acid AsF 5 .