EPR studies of VO2+ in single crystals of ZnSO4⋅7H2O and certain polycrystalline sulfates

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Abstract
EPR studies of vanadyl doped ZnSO4⋅7H2O are reported. Vanadyl is found to have fixed orientations in the lattice and there are two magnetically inequivalent complexes in the lattice. The angular variation of the spectra is studied in the crystallographic a b, b c, and a c planes. The principal values of g and A and the direction cosines which the principal axes make with the crystallographic axes are found. Vanadium enters the lattice substitutionally in the place of Zn2+ and gets bonded to five water molecules of the lattice to form a stable [VO(H2O)5]2+ complex. The results obtained from the EPR studies of the polycrystalline samples of vanadyl doped Mg(NH4)2(SO4)2 ⋅6H2O, K2SO4, and 3CdSO4⋅8H2O are also reported. The spectra are analyzed using a spin‐Hamiltonian corresponding to tetragonal symmetry. In the optical absorptionspectrum of vanadyl doped ZnSO4⋅7H2O two bands are observed in the visible region which are attributed to d–d transitions. The EPR results in conjunction with the optical results give the spin orbit coupling constant of vanadium. A semiempirical molecular orbital approach is used and the bonding parameters are estimated. The data reported in the literature for VO2+doped crystals are taken and the bonding parameters are calculated. The EPR results are correlated with the bonding parameters. The observed changes in g and A are correlated to the ligand properties. The anisotropy in g is correlated to the ligand field strength. The isotropic contact term is related to the bonding coefficient β2. The deviations in β2 2 values from the expected values are explained by considering the delocalization of the unpaired electron on to the ligand orbitals. β1 2 value is found to indicate the delocalization in the σ system. A plot of κ against β1 2 gives a straight line.

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