An AB initio molecular orbital study of the structure, energetics and bond activation of Al + complexes

Abstract

The structures and stabilities of Al + complexes of mono- and bidentate bases have been examined by ab initio molecular orbital theory. Equilibrium structures were obtained at the 6-31G ∗ level and correlation effects were evaluated at the fourth-order (MP4SDTQ) Møller-Plesset theory. The structures of the Al + complexes investigated closely resemble those of the corresponding protonated species rather than those of analogous Li + complexes. We have shown that the Al + − base interaction, although essentially electrostatic, has some covalent component through the contribution of the low-lying empty p orbitais of Al +. Our results also show that a correct description of these interactions requires the inclusion of polarization functions in the basis set. A topological analysis of the electronic charge density of the complexes and the corresponding neutral bases permits quantitative discussion of both substituent effects on the complex stability and bond activation within the base. Charge redistribution of the base upon Al + association is in agreement with the calculated shift for the stretching frequencies of the A-B bond.