The molecular structures of the gaseous dimeric molecules Me2Ga(µ-H)2GaMe2 and Me2Ga(µ-Cl)2GaMe2 as determined by electron diffraction

Abstract

The structures of gaseous dimethylgallane and dimethylgallium chloride have been determined by electron diffraction. The results indicate that the predominant vapour species at low pressures and temperatures of 290–350 K are dimeric molecules with diborane-like structures, Me₂Ga(µ-X)₂GaMe₂(where X = H or Cl), with heavy-atom skeletons conforming to D_2h symmetry. Salient structural parameters in the r_a structures are: (i) for [Me₂GaH]₂, r(Ga ⋯ Ga) 261.0(0.5), r(Ga–C) 195.4(0.4), and r(Ga–H_b) 170.8(1.4) pm; Ga–H_b–Ga 99.6(1.4) and C–Ga–C 123.2(1.5)°; (ii) for [Me₂GaCl]₂, r(Ga ⋯ Ga) 330.3(1.9), r(Ga–C) 194.6(0.3), and r(Ga–Cl_b) 237.8(0.4) pm; Ga–Cl_b–Ga 88.0(0.9) and C–Ga–C 132.1 (2.7)°(‘b’ denotes a bridging atom). Dimethylgallane thus represents the first gallium hydride containing a Ga(µ-H)₂Ga bridging unit to be characterised structurally; it is notable for the shortness of the Ga[graphic omitted]Ga distance. The two molecules invite structural comparisons with related systems like [Me₂EH]₂(E = B or Al), [Me₂AlCl]₂, and Ga₂Cl₆.