M.-Q. Kuang

Investigations of the EPR parameters for Cu2+ in [Cu(ipt)(dap)H2O]n•nH2O

The electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) for Cu2+ in [Cu(ipt)(dap)H2O]n•nH2O (ipt is isophthalic acid, dap–1,3-diaminopropane) are theoretically investigated from the high order perturbation formulas of these parameters for a 3d9 ion in a rhombically elongated octahedron. The ligand orbital and spin-orbit coupling contributions are included from the cluster approach because of strong covalency of the system. The nearly axial anisotropies of the g factors and hyperfine structure constants are correlated to the significant elongation distortion of the five-fold coordinated Cu2+ (in a distorted square pyramidal [CuN2O3] group). Nevertheless, the perpendicular anisotropies arising from the nonequivalent planar ligands are largely concealed by the experimental uncertainties. The theoretical analysis of the EPR behaviours for [Cu(ipt)(dap)H2O]n•nH2O would be helpful to understand the local structures and properties of this and relevant systems.

Theoretical studies of the spin Hamiltonian parameters and local structures for Ag 2+ in AgCl and KCl crystals

The spin Hamiltonian parameters (g factors, hyperfine structure constants and superhyperfine parameters) and local structures for Ag2+ centers in AgCl and KCl crystals are theoretically studied using the high-order perturbation formulas for a tetragonally elongated 4d9 cluster. The impurity centers undergo relative elongations (≈0.05 Å and 0.23 Å for Ag2+ in AgCl and KCl, respectively) along the C4 axis owing to the Jahn–Teller effect. All the calculated spin Hamiltonian parameters show good agreement with the experimental data, and the ligand contributions to the spin Hamiltonian parameters are important and should be taken into account. The unpaired spin densities in the superhyperfine parameters are determined from molecular orbital coefficients based on the cluster approach, instead of being taken as the adjustable parameters in the previous treatments. Increasing tetragonal elongation from AgCl to KCl is attributed to a decrease in chemical bonding (or lower force constant) with increasing Ag2+–Cl distance.

Studies on the g -factors of the copper(II)–oxygen compounds

The g factors for Cu2+ in meta-zeunerite (Cu(UO2)2(AsO4)2·3H2O), kroehnkite (Na2Cu(SO4)2·2H2O), copper benzoate (Cu(PhCO2)2·3H2O) and diaboleite (Pb2Cu(OH)4Cl2) of the tetragonal phase are uniformly treated by high order perturbation formulas for 3d9 ions in tetragonally elongated octahedra. The calculation results are in good agreement with the observed values and systematically analyzed in view of the local structures around Cu2+. The g anisotropies Δg (= g‖−g⊥) are largely ascribed to the local tetragonal elongations of the Cu2+ sites, characterized by the relative elongation ratios (R‖−R⊥)/R̅ ≈ 19%, 21%, 27% and 30% for metazeunertie, kroehnkite, copper benzoate and diaboletie, respectively. The anomalous valley (minimum) of relative g anisotropy for copper benzoate is attributed to the modification of the Cu2+ electronic states due to the phenyl ring. The ligand orbital contributions are found to be significant due to covalency, and should be taken into account. The present study would be helpful to the unified investigations of structures and properties of the copper oxygen compounds.