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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

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posted on 2009-02-18, 00:00 authored by Simon Aldridge, Anthony J. Downs, Christina Y. Tang, Simon Parsons, Michael C. Clarke, Russell D. L. Johnstone, Heather E. Robertson, David W. H. Rankin, Derek A. Wann
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, MenH3−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 MenH3−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 MenH3−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.