Ab Initio Characterization of [H3N·BH3]2, [H3N·AlH3]2, and [H3N·GaH3]2

The dimers of [H 3 N·BH 3 ] 2, [H 3 N·AlH 3 ] 2, and [H 3 N·GaH 3 ] 2 are characterized as head-to-tail complexes with intermolecular H−H hydrogen bonding. In the case of [H 3 N·BH 3 ] 2, that hydrogen bonding is bifurcated resulting in four short (N)H−H(B) distances. For both [H 3 N·AlH 3 ] 2 and [H 3 N·GaH 3 ] 2, there are only two short (N)H−H(Al/Ga) distances, although the four-atom linkage remains far from linear. The binding energies that are calculated at the MP2 level of theory using polarized-double-ζ basis sets are −15.1, −11.8, and −10.7 kcal/mol for [H 3 N·BH 3 ] 2, [H 3 N·AlH 3 ] 2, and [H 3 N·GaH 3 ] 2, respectively. These energies appear converged to within 1 kcal/mol with respect to larger basis sets and more complete accounting for electron correlation effects. Binding energies from density functional calculations are within 0.3 kcal/mol of the MP2 results. All-electron and effective-core-potential basis sets for gallium provide similar predictions.