Calculation of spin and charge densities in hexaaqua transition-metal(II) ions and their comparison with experiment

Abstract

All-electron calculations using the DV-Xα implementation of the local-density-approximation formalism are presented for the hexaaqua M^II ions of the first transition series from V^II to Zn^II. The experimental C_i symmetry geometries and limited basis sets are employed. The results are compared with the X-ray and polarised neutron diffraction experiments, which yield real-space charge and spin distributions respectively, by means of maps and orbital population analyses. Although the calculations on the one hand and the experiments on the other have limitations in the confidence with which interpretations can be made for individual members, the comparison of trends across the series of metals proves valuable. Both calculations and experiments reflect the importance of the effects of the Jahn–Teller distortions for the Cr^II and Cu^II cases and illustrate the effects of covalence. The calculations support interpretations of the experimental data which emphasise the role of spin polarisation; it is a major feature of the electron distributions in the ions of the first transition series. It is indeed responsible for the repeated observation that the transfer of spin population by covalence in the metal–ligand bonding is much less than that of charge. This confirms the long-obvious statement that single configuration Hartree–Fock theory is an unsatisfactory basis for the description of bonding in transition-metal complexes. The experimental observation that the low symmetry environment of the hexaaqua M^II ions in the salts studied has little effect on the details of the electron distribution, apart, of course from the Jahn–Teller affected cases of Cr^II and Cu^II, and the π-orbitally degenerate Fe^II and Co^II ions, is supported by the calculations. The fact that similar calculations have been made for the entire series of metal(II) ions experimentally available is of more importance than is the loss of accuracy which follows from the limited basis sets used for the individual cases.