In this work, the electron paramagnetic resonance (EPR) parameters g factors g// and g?¢???´ and the hyperfine structure constants A// and A?¢???´ of a tetragonal VO2+ center in [NH4H3(C2O4)] .H2O crystal are theoretically studied from the high order perturbation formulas of these parameters for a 3d1 ion in tetragonal symmetry (compressed octahedron). In these formulas, the contributions to the spin Hamiltonian parameters from the s-and p-orbitals as well as the spin-orbit coupling coefficient of the ligands are taken into account and the energy seperations are correlated with the geometrical relationship of present studied tetragonal cluster. The calculated EPR parameters are in good agreement with the experimental data. The results are discussed.
