Fluoridobromate(V)-hydrogen fluoride cocrystals

Cocrystals of BrF5 and HF2- salts have been obtained for the first time in the form of the two compounds [NMe4][(BrF5)6(HF2)] and Cs2[(BrF5)6(HF2)(H2F3)]. These compounds are formed when hydrogen fluoride is present in reactions of BrF5 and a fluoride ion source, such as [NMe4]F or CsF. Here we present the crystal structures of the compounds, complemented by quantum chemical solid-state calculations, and our Raman spectroscopic investigations on the compound [NMe4][(BrF5)6(HF2)]. The cocrystals contain discrete [HF2]- and [H2F3]- anions, which are coordinated by BrF5 molecules via their F atoms. The propeller-like coordination of an F atom by three BrF5 molecules, as known from the [Br3F16]- anion, appears as a recurring structural motif in these compounds.