Interpretation of the Electron Paramagnetic Resonance Spectra of Copper(II)–Tyrosine Complex

The electron paramagnetic resonance (EPR) spectra of [Cu(l-tyrosine)2]n (CuA) were interpreted based on the fourth-order perturbation treatments where the contributions due to the local distortion, ligand orbit and spin-orbit coupling were included. The calculated band transitions ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}}$ to dxy (≈16412 cm−1) and ${{\text{d}}_{{{\text{z}}^2}}}$ (≈14845 cm−1) agree well with the band analysis results ${\text{(}}{{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xy}}}}$≈16410 and ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{{\text{z}}^2}}}$≈14850 cm−1). The unresolved separations ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xz}}}}$ and ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{yz}}}}$ in the absorption spectra were evaluated as 26283 and 26262 cm−1, respectively. For CuA, copper chromophores in 1,3-diaminorpropane isophtalate copper(II) complex (CuB) and N-methyl-1,2-diaminoetaane-bis copper(II) polymer (CuC), the transition ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xy}}}}$ (=E1≈10Dq) suffered an increase with a decrease in R̅L which was evaluated as the mean value of the copper-ligand bond lengths. The correlations between the tetragonal elongation ratio ρ (=(Rz–R̅L)/R̅L) (or the ratio G=(gz–ge)/((gx+gy)/2–ge)) and the g isotropy gav (=(gx+gy+gz)/3) (or the covalency factor N) for CuA, CuB and CuC were acquired and all the results were discussed.