(μ -F)(BrF ) ] - An Unprecedented Molecular Fluoridobromate(V) Anion in Cs[Br F.

The reaction of Cs[BrF ] with BrF gave the compound Cs[Br F ] with the unprecedented propeller-shaped, C -symmetric [(μ -F)(BrF ) ] anion. All other currently known fluoridobromates(V) contain only octahedral [BrF ] anions, which, unlike the related [IF ] anions, never exhibited stereochemical activity of the lone pair on the Br atoms. Despite the same coordination number of six for the Br atom in the [BrF ] and [(μ -F)(BrF ) ] anions, the longer μ -F-Br bonds provide additional space, allowing the lone pairs on the Br atoms to become stereochemically active. Cs[Br F ] was characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical calculations for both the solid-state compound and the isolated anion at 0 K. Intrinsic bond orbital calculations show that the μ -F-Br bond is essentially ionic in nature and also underpin the stereochemical activity of the lone pairs of the Br(V) atoms.