The Existence of Hexafluoroarsenic(V) Acid

The homogeneous mixture of anhydrous hydrogen fluoride a HF and antimony pentafluoride AsF 5 is known as a superacidic system. The high acidity is derived from the formation of [H 2 F] + [AsF 6 ] − . No experimental evidence exists for the existence of the free acid molecule HAsF 6 . The reaction of trimethylsilyl N , N ‐dimethylcarbamate in the binary system a HF/AsF 5 led to decomposition of trimethylsilyl N , N ‐dimethylcarbamate at −50 °C to dimethylammonium hexafluoridoarsenate and cocrystallization of HAsF 6 . The single‐crystal X‐ray structure displays an HAsF 6 molecule involved in an asymmetric hydrogen bridge to the hexafluoridoarsenate anion. As a result of the incalculable situation in the crystal lattice, the molecular structure of HAsF 6 is calculated by quantum chemical structure optimization of the extreme cases of [FHF‐AsF 5 ] − (strong hydrogen bond) and HAsF 6 (no hydrogen bond) at the PBE1PBE/6‐311G(3df,3pd) level of theory.