Protonated decafluorobenzophenone and the decafluorobenzophenone-arsenic pentafluoride adduct

The reaction of decafluorobenzophenone [perfluorobenzophenone, (C₆F₅)₂CO] with AsF₅ in anhydrous HF yields the protonated salt [bis(2,3,4,5,6-pentafluorophenyl)methylidene]oxidanium hexafluoridoarsenate, (C₆F₅)₂COH⁺[AsF₆]^-, whereas its reaction with AsF₅ in SO₂ affords the Lewis acid-base adduct decafluorobenzophenone-arsenic pentafluoride, (C₆F₅)₂CO·AsF₅. 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 (C₆F₅)₂COH⁺[AsF₆]^- features a short O-H...F hydrogen bond between the cation and the anion, and the crystal structure of (C₆F₅)₂CO·AsF₅ represents a rare example of a ketone coordinated to the strong Lewis acid AsF₅.