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The electron paramagnetic resonance (EPR) parameters (g factors g_{i} and the hyperfine structure constants A_{i}, i = x, y, z) are interpreted by using the perturbation formulae for a 3d^{9} ion in rhombically (D_{2h}) elongated octahedra. In the calculated formulae, the crystal field parameters are set up from the superposition model, and the contribution to the EPR parameters from the admixture of d-orbitals in the ground state wave function of the Cu^{2+} ion was taken into account. Based on the calculation, local structural parameters of the impurity Cu^{2+} center in Cd_{2}(NH_{4})_{2}(SO_{4})_{3} (CAS) crystal were obtained (i.e., R_{x} ≈ 2.05 Å, R_{y} ≈ 1.91Å, R_{z} ≈ 2.32 Å). The theoretical EPR parameters based on the above Cu^{2+}-O^{2-} bond lengths in CAS crystal show a good agreement with the observed values. The results are discussed.

On the basis of the perturbation formulas for a d^1 configuration ion in a tetragonal crystal field, the three optical absorption bands and electron paramagnetic resonance (EPR) parameters (g factors g_i and hyperfine structure constants A_i for i = || and ⊥, respectively) of VO^{2+} in Na_3C_6H_5O_7·2H_2O (TSCD) single crystals were studied using the perturbation theory method. By simulating the calculated optical and EPR spectra to the observed values, local structure parameters and negative signs of the hyperfine structure constants A_i of the octahedral (VO_6)^{8-} cluster in TSCD single crystal can be obtained.