Crystal Structure of Bis(triethylammonium)c/0so-decahydrodecaborate, [(C2H5)3NH]2[B10H10]

The crystal structure of bis(triethylammonium)c/o5o-decahydrodecaborate [bis(triethylammonium)decaboranate(lO)], [(CaHs^NHMBioHio], was determined and refined (space group Pmmn, no. 59, a = 989.7, b = 1333.7, c = 903.7 pm). The compound is a versatile starting material for many substances containing the [BioHio]2entity and its derivatives. The c7oso-[BioHio]2cluster is a bicapped square antiprism which is only slightly distorted. Its deviation from D ^ symmetry is smaller than that of the Bio cages in every other compound containing this entity that have been structurally characterised. The presence of additional (N )H ---B 3 interactions in form of multiple-centre bonds between the cations and the anions, which were postulated earlier and which should influence the cage symmetry, could not be confirmed. At 55 °C, the transition into a high temperature phase was investigated by X-ray powder diffraction. The high temperature phase crystallises in the tetragonal crystal system (a = 946.9, c = 1351.0 pm).