Theory of antiferromagnetic exchange interaction for mixed-valent FeIIIFeII spin cluster in model complex of semimethemerythrin Original Research Article

Electron spin resonance (ESR) of Cu2+ doped cadmium formate dihydrate single crystal was studied at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the spin-Hamiltonian parameters, Cu2+(I): gx=2.097±0.002, gy=2.1166±0.002, gz=2.2887±0.002 and Ax=(140±2)×10−4 cm−1, Ay=(151±2)×10−4 cm−1, Az=(239±2)×10−4 cm−1, Cu2+(II): gx=2.0843±0.002, gy=2.1045±0.002, gz=2.2742±0.002 and Ax=(141±2)×10−4 cm−1, Ay=(158±2)×10−4 cm−1, Az=(267±2)×10−4 cm−1. The ground state wave function of the Cu2+ ion in this lattice is evaluated. It is found that the ground state is predominantly |x2−y2〉. The g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex has been discussed.