Structures and Aggregation of the Methylamine−Borane Molecules, MenH3−nN·BH3(n= 1−3), Studied by X-ray Diffraction, Gas-Phase Electron Diffraction, and Quantum Chemical Calculations

Abstract

The structures of the molecules methylamine−borane, MeH₂N·BH₃, and dimethylamine−borane, Me₂HN·BH₃, have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations. The crystal structures have also been determined for methylamine−, dimethylamine−, and trimethylamine−borane, Me_nH_3−nN·BH₃ (n = 1−3); these are noteworthy for what they reveal about the intermolecular interactions and, particularly, the N−H···H−B dihydrogen bonding in the cases where n = 1 or 2. Hence, structures are now known for all the members of the ammonia− and amine−borane series Me_nH_3−nN·BH₃ (n = 0−3) in both the gas and solid phases. The structural variations and energetics of formation of the gaseous adducts are discussed in relation to the basicity of the Me_nH_3−nN fragment. The relative importance of secondary interactions in the solid adducts with n = 0−3 has been assessed by the semi-classical density sums (SCDS-PIXEL) approach.