The existence of hexafluoroarsenic(V) acid

Joachim Axhausen; Karin Lux; Andreas Kornath

doi:10.1002/anie.201308023

The existence of hexafluoroarsenic(V) acid

Angew Chem Int Ed Engl. 2014 Apr 1;53(14):3720-1. doi: 10.1002/anie.201308023. Epub 2014 Jan 20.

Authors

Joachim Axhausen¹, Karin Lux, Andreas Kornath

Affiliation

¹ Ludwig Maximilian University Munich (LMU), Department of Chemistry, Butenandtstrasse 5-13, Haus D, 81377 Munich (Germany) http://www.cup.uni-muenchen.de/ac/kornath/index.php.

PMID: 24446235
DOI: 10.1002/anie.201308023

Abstract

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.

Keywords: density functional calculations; hexafluoridoarsenic(V) acid; structure elucidation; superacid systems.