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 center dot 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. (c) 2006 Elsevier B.V. All rights reserved.