Molecular orbital study of complexes of zinc(II) with imidazole and water molecules

Abstract

Geometry optimizations and energy calculations have been performed at the density functional B3LYP level on imidazole (HL), imidazolate (L −), imidazolium (H 2L +), 3-methylimidazole, 4-methylimidazole, 5-methylimidazole, [Zn(HL)] 2+, [Zn(3-MeL)] 2+, [Zn4-Me(HL)] 2+, [Zn5-Me(HL)] 2+, [Zn(OH)] +, [Zn(H 2O)] 2+, [Zn(H 2O) 6] 2+, [Zn(H 2O)(HL)] 2+, [Zn(HL) 2] 2+, [Zn(HL) 3] 2+, [Zn(OH)(HL) 3] + and [Zn(H 2O)(HL) 3] 2+. Coordination of zinc(II) at N(1) of imidazole causes nearly the same changes in bond distances and base inner angles in the imidazole framework as protonation does. The ZnO and ZnN distances in [Zn(H 2O) m (HL) n ] 2 complexes become longer as the number of coordinating ligands increases. Calculated bond dissociation energies show that HL is more strongly bound than H 2O to Zn(II) and its complexes. The population analysis indicates that the imidazole ligand transfers charge to Zn(II) and is a much more efficient charge neutralizer than H 2O. The analysis further indicates that imidazole is very strongly polarized by Zn(II). Intermolecular ZnN stretching and ZnNC bending bands in [Zn(HL)] 2+ are weak in intensity; the former is red-shifted upon coordination of H 2O. The OH stretching frequencies are blue-shifted when imidazole is coordinated to [Zn(H 2O)] 2+.