Bromine Pentafluoride BrF₅, the Formation of [BrF₆]⁻ Salts, and the Stereochemical (In)activity of the Bromine Lone Pairs

AbstractBrF5 can be prepared by treating BrF3 with fluorine under UV light in the region of 300 to 400 nm at room temperature. It was analyzed by UV‐Vis, NMR, IR and Raman spectroscopy. Its crystal structure was redetermined by X‐ray diffraction, and its space group was corrected to Pnma. Quantum‐chemical calculations were performed for the band assignment of the vibrational spectra. A monoclinic polymorph of BrF5 was quantum chemically predicted and then observed as its low‐temperature modification in space group P21/c by single crystal X‐ray diffraction. BrF5 reacts with the alkali metal fluorides AF (A=K, Rb) to form alkali metal hexafluoridobromates(V), A[BrF6] the crystal structures of which have been determined. Both compounds crystallize in the K[AsF6] structure type (R , no. 148, hR24). For the species [BrF6]+, BrF5, [BrF6]−, and [IF6]−, the chemical bonds and lone pairs on the heavy atoms were investigated by means of intrinsic bond orbital analysis.