Theoretical calculations of spin-Hamiltonian parameters for the (MoOX5)2− (X=Cl, Br) metallic complexes in solution or frozen-glass

The spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) of the (MoOX5)2− (X=Cl, Br) metallic complexes in solution or frozen-glass are calculated from the high-order perturbation formulas based on the two-mechanism model. In these formulas, the contributions to spin-Hamiltonian parameters due to both the widely-applied crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (which is neglected in CF theory) are taken into account, and the needed CF and CT energy levels are obtained from the optical spectra. The calculated results with two adjustable parameters are in reasonable agreement with the experimental values. The calculations show that (i) the relative importance of CT mechanism in (MoOBr5)2− metallic complexes is larger than that in (MoOCl5)2− ones because of the stronger covalence of Mo5+-Br− combination, and (ii) in both (MoOCl5)2− and (MoOBr5)2− metallic complexes, the contributions to spin-Hamiltonian parameters due to CT mechanism should also be taken into account because of the high valence state of Mo5+ ion.