An EPR and optical absorption study of VO2+ ions in sodium hydrogen oxalate monohydrate (NaHC2O4·H2O) single crystals

Electron paramagnetic resonance of VO2+ doped sodium hydrogen oxalate monohydrate (NaHC2O4·H2O) single crystals and powders are examined at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes namely ac*, b*c* and ab* indicate four different VO2+ complexes with intensity ratios of 4:2:1:1. It is found from the EPR analysis that the Na+ ions are replaced with the substitutional magnetically inequivalent VO2+ ions. The powder spectrum also clearly indicates four different VO2+ complexes, confirming the single crystal analysis. Crystalline field around the VO2+ ion is nearly axial. The optical absorption spectrum show two bands centered at 15 408 and 12 453 cm−1. Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.