Theoretical studies of the EPR parameters and local structures for Cu

Local structure and electron paramagnetic resonance (EPR) parameters (the g factors, gi, and the hyperfine structure constants Ai, i = x, y, z) for the impurity Cu2+ centres in a (CH3)2NH2Al(SO4)2·6H2O (DMAAS) crystal are theoretically investigated by using the high-order perturbation formulas of these parameters for a 3d9 ion in an orthorhombically elongated octahedron. The related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way. From the studies, the four planar Cu2+-O2− bond lengths are found to experience the relative variation δR ( ≈0.033 and 0.063 Å) along the X- and Y-axes, while the two parallel bond lengths may undergo relative elongation ΔZ (≈0.058 and 0.052 Å) along the C2 axis for the studied Cu2+ centres I and II, respectively, due to the Jahn-Teller effect. The theoretical EPR parameters based on the above local lattice distortions agree well with the experimental data. The results are discussed