Ab initio calculations of monosubstituted (CH3OH, CH3SH, NH3) hydrated ions of Zn2+ and Ni2+

Model complexes of hydrated zinc(II) and nickel(II) cations with one water substituted for methanol, methanethiol, and ammonia are studied. The accura cy of various computational methods, influence of the basis set, and the ro le of the coordination geometry are investigated. It is shown that density functional theory calculations (B3LYP functional) yield very accurate resul ts, but the basis set of at least triple-zeta quality with polarization and diffuse functions should be used. The calculated mean absolute difference between DFT and QCISD(T) reaction energies for the substitution reactions o n the central metal ion is less than 0.5 kcal mol(-1) It is also observed t h:lt the metal-ligand distances and the reaction energies of monosubstitute d hydrated complexes of metal ions are strongly dependent on the number of ligands in the first coordination sphere and the coordination geometry. The implications of having a reliable, accurate, and relatively fast method fo r the calculation of transition metal complexes are discussed. Several appl ications oriented toward the interactions of transition metals with the ami no acid residues are mentioned.