Molecular structures of tetraborane(10) derivatives: Ab initio calculations for (CH₃)₂MB₃H₈ (M = B, Al, Ga or In) and gas-phase electron diffraction studies of (CH₃)₂AlB₃H₈ and (CH₃)₂GaB₃H₈

Structural trends in the family of compounds (CH₃)₂MB₃H₈ (M = B, Al, Ga or In) have been investigated by ab initio molecular orbital calculations. In addition, the gas-phase molecular structures of(CH₃)₂AlB₃H₈ and (CH₃)₂GaB₃H₈ have been re-determined by gas-phase electron diffraction using the SARACEN method of structural analysis. Salient structural parameters (r_α⁰) for the aluminium and gallium compounds were found respectively to be: r-[B(1)⋯M(2)] 231.6(7), 234.2(8); r[B(1)-B(3)] 178.2(12), 178.9(23); r[B(1)-B(4)] 184.4(10), 184.3(23); r[B(1)-H(1,2)] 124.6(11), 121.6(18); r[M(2)-H(1,2)] 182.5(13), 186(6); r[B(1)-H(1,4)] 126.2(11), 122.9(18); r[B(4)-H(1,4)] 142.6(11), 140(3) pm; butterfly angle 123.8(20), 119.8(13)°.