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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)

A new method of synthesis of o- and m-carboranyl-B-thiols and o- and m-carboranyl-B,B'-dithiols via the electrophilic sulfuration of o, m-carboranes with S2Cl2 in the presence of AlCl3 is described. The reaction of o-carborane with excess S2Cl2 in the presence of AlCl3 gives B,B',B″,B″′-tetrathiol-o-carborane. Various chemical conversions of carborane sulfur derivatives are studied. A description is made of carboranyl derivatives of di-, tetra- and hexavalent sulfur, such as sulfenyl chlorides, thiocyanates, disulfides, alkyl- and aryl sulfides, aryl sulfones and aryl sulfoxides. 9-m-Carboranylsulfinic acid was found to readily disproportionate to thiosulfonate and sulfonic acid. The chemical behaviour of o- and m-carboranyl sulfur derivatives in which the sulfur atom is σ-bound to the six-coordinated boron atom was also found to be similar to that of organic sulfur derivatives.