Electronic structure and optical spectra of transition metal complexes by the effective Hamiltonian method

A semiempirical effective Hamiltonian treatment is proposed for transition metal complexes, taking into account d-electron correlations, weak covalency of the metal-ligand bonds and the electronic structure of the ligand sphere. The technique uses the variation wave function which differs from the usual Hartree-Fock antisymmetrized product of molecular orbitals extended over the whole complex. The scheme is implemented and parameters describing the metal-ligand interactions are adjusted to reproduce d-d-excitation spectra of a number of octahedral MF₆^4- (M=Mn, Fe, Co, Ni) anions, Mn(FH)₆²⁺ cation, CoCl₆^4- anion, and a tetrahedral CoCl₄^2- anion. The values of the parameters are reasonable, thus confirming the validity of the proposed scheme.