Theoretical studies of the spin-Hamiltonian parameters of the oxycation MoO3+ in (NH4)2MoOCl5 and K2MoOF5 single crystals

Theoretical formulae for the spin-Hamiltonian (SH) parameters (g tensor g//, g⊥ and hyperfine structure A tensor A//, A⊥) of the ground state of oxycation MoO3+ in [MOX5]2− (M=Mo5+, Cr4+, V3+, X=F−, Cl− or Br− ) complexes are derived by the high-order perturbation method within the frame of molecular orbital (MO) scheme. In those formulae, the contributions to the SH parameters arising both from the crystal field (CF) and charge transfer (CT) excitations are taken into account, which are derived up to the third and second order, respectively. Those formulae are applied to calculate the SH of the oxycation MoO3+ in (NH4)2MoOCl5 and K2MoOF5 single crystals by the best match method, and the calculated results are in good agreement with the experimental data. The investigations show that the charge transfer mechanism play a decisive role in the understanding for the SH parameters for 4d1 ions in crystals with the strong coordinate covalence, especially for anomalously experimental results g//>g⊥ which cannot be explained by the traditional CF approximation alone. The MO coefficients are determined and the results are discussed.