Vibrational Spectrum and Electronic Structure of the [B11H11]2– Dianion

The vibrational spectrum, geometrical structure and electron-density distribution (EDD) of the formally closo (2n+2)-electron cluster species [B11H11]2– have been studied. The presence of two low-frequency vibrational modes is evidence of cluster nonrigidity. A rationale for this lies in the results of EDD calculations which show that the polyhedron lacks two-centre edge-localized B–B bonds of the 6k–5k type and that its surface exhibits two six-membered rings with low electron density. Thus, the polyhedron does not consist of deltahedral faces only and therefore does not have a genuine closo structure. The data obtained also allow further elucidation of the “diamond-square-diamond” mechanism as commonly applied to the fluxionality of [B11H11]2– in solution.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)