MOLECULAR-ORBITAL STUDY OF COMPLEXES OF ZINC(II) WITH IMIDAZOLE AND WATER-MOLECULES

Geometry optimizations and energy calculations have been performed at the density functional B3LYP level on imidazole (HL), imidazolate (L-) , imidazolium (H2L+), 3-methylimidazole, 4-methylimidazole, 5-methylim idazole, [Zn(HL)](2+), [Zn(3MeL)](2+) [Zn(4-Me(HL))](2+), [Zn(5-Me(HL) )](2+), [Zn(OH)](+), [Zn(H2O)](2+), [Zn(H2O)(6)](2+), [Zn(H2O)(HL)](2), [Zn(HL)(2)](2+) [Zn(HL)(3)](2+), [Zn(OH)(HL)(3)](+) and [Zn(H2O)(HL )(5)](2+). Coordination of zinc(II) at N(1) of imidazole causes nearly the same changes in bond distances and base inner angles in the imida zole framework as protonation does. The Zn-O and Zn-N distances in [Zn (H2O)(m)(HL)(n)](2) complexes become longer as the number of coordinat ing ligands increases. Calculated bond dissociation energies show that HL is more strongly bound than H2O to Zn(II) and its complexes. The p opulation analysis indicates that the imidazole ligand transfers charg e to Zn(II) and is a much more efficient charge neutralizer than H2O. The analysis further indicates that imidazole is very strongly polariz ed by Zn(lI). 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 H2O. The O-H stretching frequencies are blue-shifted w hen imidazole is coordinated to [Zn(H2O)](2+). (C) 1997 Elsevier Scien ce B.V.