The Existence of Hexafluoroarsenic(V) Acid

The homogeneous mixture of anhydrous hydrogen fluoride aHF and antimony pentafluoride AsF₅ is known as a superacidic system. The high acidity is derived from the formation of H₂F]⁺ AsF₆]^?. No experimental evidence exists for the existence of the free acid molecule HAsF₆. The reaction of trimethylsilyl N,N‐dimethylcarbamate in the binary system aHF/AsF₅ led to decomposition of trimethylsilyl N,N‐dimethylcarbamate at ?50 °C to dimethylammonium hexafluoridoarsenate and cocrystallization of HAsF₆. The single‐crystal X‐ray structure displays an HAsF₆ 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 HAsF₆ is calculated by quantum chemical structure optimization of the extreme cases of FHF‐AsF₅]^? (strong hydrogen bond) and HAsF₆ (no hydrogen bond) at the PBE1PBE/6‐311G(3df,3pd) level of theory.