The Fate of CrO₂F₂ in Highly Acidic Media: Fluoride Loss, O-Protonation or F-Protonation?

Abstract

Theoretical calculations at the DZ/SCF level are reported for CrO₂F₂ and for three of its possible products of interaction with highly acidic anhydrous hydrogen fluoride. The molecular structure and vibrational frequencies of CrO₂F₂ are reproduced with reasonable accuracy. It seems unlikely that CrO₂F⁺ is formed from CrO₂F₂ in anhydrous hydrogen fluoride, since that ion is structurally unstable as an isolated entity. While the thermodynamic stabilities of CrO (OH)F₂⁺ and CrO₂F(FH)⁺ are almost identical, comparison of calculated vibrational frequencies with the experimental results of O'Donnell and coworkers suggests that the product of interaction of CrO₂F₂ with anhydrous hydrogen fluoride/SbF₅ is CrO₂F(FH]⁺, rather than CrO (OH)F₂⁺. However, the Cr-F(H) bond in CrO₂F(FH)⁺ is so much longer than the bond to the unprotonated fluorine that CrO₂F(FH)⁺ is perhaps best described as a CrO₂F⁺ ion strongly solvated by one HF molecule.