An EPR study on VO2+ and Mn2+ ions in some zeolites

Abstract

The electron paramagnetic resonance (EPR) of hydrated VOSO4 . 3H(2)O and MnCl2 . 2H(2)O, adsorbed on the synthetic zeolites 3A, 4A, 5A and 13X of pore diameters 0.3, 0.4, 0.5, and 1.0 nm, respectively, and the natural zeolites heulandite and clinoptilolite was investigated. The spectra indicated that the coordination structures are VO(H2O)5(2+) and Mn(H2O)(6)(2+) and that their EPR line widths vary with the pore diameters and the surface areas of the zeolites. The spectra of VO(H2O)(5)(2+) in natural zeolites at room temperature display an isotropic behavior and therefore indicate that the water ligands are mobile. The EPR spin Hamiltonian parameters, the molecule orbital constant beta(2)*(2), and the Fermi contact term K-eff were determined and are discussed. The spectra of Mn(H2O)(6)(2+) for narrow-pore zeolites indicate the existence of mobile and immobile water, whereas for wide-pore and natural zeolites they indicated the existence of only mobile water. The obtained Mn(H2O)(6)(2+) spectra are discussed.