Charge density and spectra of dichlorotetrakis(thiourea) nickel(II): an ab initio discrete variation Xα calculation

Abstract

An ab initio calculation using the discrete variational Xα implementation of Hartree–Fock–Slater theory, with frozen cores, has been performed on the compound [Ni(tu)₄Cl₂](tu = thiourea) in the experimental geometry, and the results compared with the optical spectra, the magnetic susceptibilities, and the charge-density distribution. The treatment provides a better account of the experimental observations than earlier analyses using empirical ligand-field models. It suggests a reassignment of some features of the spectra, and supports the quite appreciable covalence, involving both σ- and π-charge flows, that is observed in the charge-density study. The reduction in the electron-repulsion parameters inferred in our interpretation of the spectra is consistent with this large covalence.