[(& mu;(3)-F)(BrF5)(3)](-) - An Unprecedented Molecular Fluoridobromate(V) Anion in Cs[Br3F16]

The reaction of Cs[BrF6] with BrF5 gave the compound Cs[Br3F16] with the unprecedented propeller-shaped, C-3-symmetric [(& mu;(3)-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 [(& mu;(3)-F)(BrF5)(3)](-) anions, the longer & mu;(3)-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 & mu;(3)-F-Br bond is essentially ionic in nature and also underpin the stereochemical activity of the lone pairs of the Br(V) atoms.

Automated summary

The reaction of Cs[BrF6] with BrF5 resulted in the formation of Cs[Br3F16], a compound with an unprecedented propeller-shaped, C-3-symmetric [(& mu;(3)-F)(BrF5)(3)](-) anion. Unlike other fluoridobromates(V), which contain only octahedral [BrF6](-) anions, the [(& mu;(3)-F)(BrF5)(3)](-) anion exhibits stereochemical activity of the lone pair on the Br atoms due to the longer & mu;(3)-F-Br bonds. Cs[Br3F16] was characterized using various techniques and quantum-chemical calculations support the stereochemical activity of the Br(V) atoms' lone pairs.