VO2+ doped potassium dihydrogen phosphate (KH2PO4) and potassium tetraoxalate (KH3C4O8 ·
2H2O) single crystals and powders are examined by electron paramagnetic resonance and optical absorption
spectroscopy. Angular variations of KH2PO4 and KH3C4O8 ·2H2O single crystals show four
and two different VO2+ sites, respectively. The local symmetry of VO2+ complexes is nearly axial
for both host crystals. The optical absorption spectra show three bands. Spin Hamiltonian parameters
are measured and molecular orbital coefficients are calculated by correlating EPR and optical absorption
data for the central vanadyl ion.