EPR and optical absorption studies of vanadyl ions in potassium oxalate monohydrate

Electron paramagnetic resonance (EPR) studies are reported on vanadyl (VO2+) ions in potassium oxalate monohydrate (POM) single crystals at room temperature. The results indicate that the paramagnetic impurity takes up an interstitial site in the lattice. The angular variation of EPR spectra in three mutually perpendicular planes are used to determine the spin Hamiltonian parameters and the values obtained are: g(x) = 2.0153 +/- 0.0002, g(y) = 1.9489 +/- 0.0002, g(z) = 1.9155 +/- 0.0002 and A(x) = (63 +/- 2) x 10(-4) cm(-1), A(y) = (92 +/- 2) x 10(-4) cm(-1), A(z) = (193 +/- 2) x 10(-4) cm(-1). The optical absorption spectrum ofVO(2+) ions in the crystal lattice is also studied at room temperature. The characteristic spectrum of the VO2+ ions has four absorption bands. The band positions are calculated using the energy expressions and compared with the observed values to confirm the transitions. The analysis of the spectrum indicates that the first three bands correspond to d-d transitions and the last band is probably charge transfer band. Crystal field parameter (Dq) and tetragonal parameters (Ds and Dt) are also evaluated. From optical and EPR data various bonding parameters are obtained and nature of bonding in the crystal is discussed. (c) 2006 Elsevier B.V. All rights reserved.