THEORETICAL-STUDY OF THE MONO-HYDRATED AND DI-HYDRATED DIVALENT IONS OF THE 1ST-ROW TRANSITION-METALS

Theoretical binding energies and M-O distances have been obtained by ab initio quantum chemical calculations performed at the modified correlated pair functional (MCPF) level on the mono- and di-hydrated divalent first-row transition metal ions, M(H2O)n2+, n = 1,2, M = Ca, Sc,...,Zn. The results are discussed in terms of electronic factors and compared with the variation of the binding energies of the hexahydrated ions, M(H2O)6.+, in order to evaluate the different effects of one or two ligands and of an octahedral ligand field. Also included is a discussion of correlation and relativistic effects, and a test of the internal water geometry, which has been carefully optimized. All dihydrated ions are linear, except Ca(H2O)22+, where the OCaO angle was found to be 130-degrees-. Strong correlations exist between binding energies and M-O distances, showing the electrostatic origin of the bonding.