EPR and optical absorption studies on VO2+ ions in sodium citrate single crystals

X-band electron paramagnetic resonance (EPR) studies of VO2+ ions in sodium citrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO2+ sites. Both the vanadyl complexes are found to take up substitutional position. The angular variation of the EPR spectra in three planes ba*, bc and ca* are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, Site I: gx = 1.9680, gy = 2.0053, gz = 1.9124, Ax = 79, Ay = 76, Az = 185; Site II: gx = 1.9650, gy = 2.0067, gz = 1.9418, Ax = 78, Ay = 70, Az = 186 × 10−4 cm−1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.