EPR and Optical Studies ofCu2+in Dodecahedral Configuration

The EPR and polarized optical spectra of copper calcium acetate hexahydrate and ${\mathrm{Cu}}^{2+}$ doped in isomorphous cadmium calcium acetate hexahydrate have been investigated in the range of temperature 300-77 °K. $g$ values in both concentrated and doped crystals are found to be the same, indicating the identical ligand fields. The spin-Hamiltonian parameters remain un-changed throughout the temperature range. The parameters are $g_{\parallel }=2.360\mathrm{}\pm 0.005$, $g_{\perp }=2.060\mathrm{}\pm 0.005$, $\left|A_{\parallel }\right|=0.0119\mathrm{}\pm 0.0002$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\left|A_{\perp }\right|=0.0013\mathrm{}\pm 0.0002$ ${\mathrm{cm}}^{-1\mathrm{}}$. Detailed study of the line-width has established the important contributions of the exchange, hyperfine, and crystal fields. The observed optical bands at 12 800 and 14 000 ${\mathrm{cm}}^{-1\mathrm{}}$ exhibit polarization and have intensities characteristic of ligand field bands. With the knowledge of relative magnitudes of $g (g_{\parallel }>g_{\perp })$, assignments of the bands have been made, consistent with the $D_{2d}$ symmetry of the ligand field. The analysis has revealed that the $3d^9-3d^{8}4p$ configuration interaction is rather small (at most 2%) in these noncentrosymmetric complexes, and the covalent metal-ligand interaction is more pronounced in the ground state than in the excited states.