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

BrF₅ 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 (Formula presented.), 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.