Abstract:
Molecular orbital calculations with HF/3-21G**, HF/6-311+G**, and MP2/6-311+G** basis sets (HF = Hartree-Fock approximation; MP2 = 2nd-order Moller-Plesset perturbation theory) have been performed on molecular clusters in the system acetate-aluminum-water. The results model the structures, energetics, and vibrational spectra of Al3+ and Al3+-acetate complexes in the aqueous phase. An octahedral to tetrahedral coordination change is predicted in the species Al3+ (OH)-m . n(H2O) [where m + n = 6] as m increases from two to three. Calculated reaction energetics for aqueous Al3+-acetate complexation compare favorably with experimental enthalpies. In addition, the possible existence of more than one configuration for each Al3+-acetate species was investigated. Theoretical vibrational spectra of the Al3+-acetate complexes provide predictions for the identification of Al3+-acetate species in aqueous solutions.