2,4-ETHANOTETRABORANE DERIVATIVES - 3 - DETERMINATION OF THE MOLECULAR-STRUCTURE OF 2,4-(T-BUTYLETHANO)TETRABORANE(10), 2,4-((BUCHCH2)-C-T)B4H8, IN THE GAS-PHASE BY ELECTRON-DIFFRACTION

The molecular structure of 2,4-(t-butylethano)tetraborane(10), 2,4-((B uCHCH2)-C-t)B4H8, in the gas phase has been determined by analysis of electron diffraction data, restrained by MP2/6-31G ab initio calculat ions. The effect of the t-butyl group is mainly to twist the C-C bond of the C2B4 'basket' by 6.6 (14)degrees, so that the local symmetry of the C2B4 fragment is reduced from C-2v to C-2. The concomitant distor tion of the B4H8 group from C-2v local symmetry is insignificant. Ab i nitio calculations at the same level are also reported for related com pounds in which the basket 'handle' is trans-(BuCHCHBut)-C-t, Me3SiCHC H2, trans-Me3SiCHCHSiMe3, cyclo-C5H8, cis-MeCHCHMe and Me2CCMe2, and f or all possible compounds with one or two terminal hydrogen atoms of t he C2H4B4H8 basket replaced by ethyl groups. (C) 1998 Elsevier Science B.V.