G2(MP2) molecular orbital study of [H3AlXH3]- (X = C, Si, and Ge) and H3AlYH3 (Y = N, P, and As) complexes

[H3AlXH3](-) (X = C, Si, and Ge) and H3AlYH3 (Y = N, P, and As) have been investigated as donor-acceptor complex types at the G2(MP2) level of theory. Both staggered and eclipsed conformations have been examined. For all complexes, the first one is found to be favored. The G2(MP2) results show that the anionic complexes are more stable than the neutral ones. They show also that this stability decreases when going from carbon to germanium for [H3AlXH3](-) complexes and from nitrogen to arsenic for H3AlYH3 complexes. The interaction diagrams prove that the evolution of complexation energy depends on the coordination mode. In fact, this is a simple "HOMO-LUMO" interaction for [H3AlXH3](-) anionic complexes, while for the H3AlYH3 neutral ones it is a result of two interaction types: interaction between "a(1)" symmetry fragments orbital (stabilizing) and interactions between "e" symmetry fragments orbital (destabilizing). A linear relationship has been established and discussed between the G2(MP2) complexation energy and the ligand G2(MP2) proton affinity, whereas no correlation has been found with the charge transfer.