[(μ₃‐F)(BrF₅)₃]⁻ – An Unprecedented Molecular Fluoridobromate(V) Anion in Cs[Br₃F₁₆]

Abstract

The reaction of Cs[BrF₆] with BrF₅ gave the compound Cs[Br₃F₁₆] with the unprecedented propeller‐shaped, C₃‐symmetric [(μ₃‐F)(BrF₅)₃]⁻ anion. All other currently known fluoridobromates(V) contain only octahedral [BrF₆]⁻ anions, which, unlike the related [IF₆]⁻ 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 [BrF₆]⁻ and [(μ₃‐F)(BrF₅)₃]⁻ anions, the longer μ₃‐F−Br bonds provide additional space, allowing the lone pairs on the Br atoms to become stereochemically active. Cs[Br₃F₁₆] 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 μ₃‐F−Br bond is essentially ionic in nature and also underpin the stereochemical activity of the lone pairs of the Br(V) atoms.