Electron Paramagnetic Resonance Studies of VO2+ Doped in KAl(SO4)2·12H2O and NH4Al(SO4)2·24H2O Single Crystals

The electron paramagnetic resonance spectra of VO2+ ions doped in KAl(SO4)2·12H2O and NH4AL(SO4)2·24H2O single crystals are studied. In both the crystals it is observed that VO2+ ion substitutes for an Al3+ ion and forms a [VO(H2O)5]2+ complex, forming a distorted octahedron with an H2O vacancy along the VO bond direction. The octahedron axes are found to coincide with the crystallographic 〈100〉 axes, indicating that the presence of VO rotates the octahedron axes so as to coincide with the crystallographic axes. The formation of the vanadyl pentahydrate complex has been further confirmed by taking an optical-absorption spectrum. By correlating the EPR and the optical-absorption data, the covalency rates of σ bonding between the vanadium atom and the equitorial ligands and of the π bonding between the vanadium atom and the vanadyl oxygen have been estimated. All the spectra are analyzed by using the usual spin-Hamiltonian method.