Closing the gap: Structural evidence for the missing hexabromide dianion [Br₆]²⁻?
Karsten Sonnenberg, Patrick Pröhm, Carsten Müller, Helmut Beckers, Simon Steinhauer, Dieter Lentz, Sebastian Riedel – 2018
The formation and experimental characterization of the first hexabromide dianion is presented. This dianion fills the last remaining gap in the series of polybromides from the tribromide [Br₃]⁻ to the undecabromide [Br₁₁]⁻. The experimental results are compared to quantum‐chemical calculations. These calculations predict—based on electrostatic interactions—a T‐structure for the hexabromide dianion, while halogen–halogen bonding favors the hockey‐stick‐like structure experimentally found in the crystal structure. The hexabromide is built of two tribromide moieties, one of which is highly asymmetric. The classification of this unique anion as hexabromide dianion is discussed. The counter ion [C₅H₁₀N₂Br]⁺ stabilizes the hexabromide dianion by additional σ‐hole interactions. The compound is fully characterized by mass spectrometry, NMR‐, IR and single crystal Raman spectroscopies as well as single‐crystal X‐ray diffraction.