Molecular structures of dimethylaluminium octahydrotriborate and dimethylgallium octahydrotriborate in the gas phase as determined by electron diffraction

Abstract

The structures of the gaseous molecules Me₂AlB₃H₈ and Me₂GaB₃H₈ have been studied by electron diffraction. Each species appears to have a skeleton analogous to that of B₄H₁₀, the metal atom being linked to each of two boron atoms of the octahydrotriborate group via a single hydrogen bridge (H_b). The following structural parameters (distances correspond to r_a) have been deduced: (i) for Me₂AlB₃H₈r(Al–C) 193.2(0.8), r(Al–B) 230.7(0.8), r(Al–H_b) 190.6(4.1) pm, C–Al–C 126.8(1.5), and the dihedral angle α defining the folding of the AlB₃ skeleton 117.6(0.7)°; (ii) for Me₂GaB₃H₈r(Ga–C) 193.0(0.7), r(Ga–B) 234.4(0.9), r(Ga–H_b) 198.9(4.8) pm, C–Ga–C 130.3(1.9), and α 117.1(0.9)°.