Crystal structure of 1-butyl-2,3-di-methyl-imidazolium dicarba-7,8-nido-undeca-borate.

In the title mol-ecular salt, C9H17N2 (+)·C2H12B9 (-), the carborane cage has a bridging B-H-B bond on the open B3C2 face. The butyl side chain of the cation adopts an extended conformation [C-C-C-C = 179.6†(1)°]. In the crystal, the imidazolium ring is almost coplanar with the open face of the carborane anion. The cations stack in the [010] direction and the dihedral angle between the imidazolium rings of adjacent cations is 68.45†(6)°. The butyl chains extend into the space between carborane anions.