Impurity in three substitutional locations: Single-crystal EPR study of VO(II) in zinc maleate tetrahydrate

Single-crystal EPR study of VO(II)-doped zinc maleate tetrahydrate has been carried out at room temperature. Four types of impurities have been identified in the single-crystal spectra with intensity ratio of 11:5:2:1. However, the analysis has been done only for the three most intense resonances. The evaluated spin Hamiltonian parameters (A in units of mT) from single-crystal rotations are site I: gxx=1.981, gyy=1.971, gzz=1.939; Axx=7.43, Ayy=7.70, Azz=18.7; site II: gxx=1.973, gyy=1.966, gzz=1.939; Axx=7.08, Ayy=7.22, Azz=18.5; site III: gxx=1.978, gyy=1.977, gzz=1.951; Axx=7.11, Ayy=7.32, Azz=18.3.The powder spectrum gives only one set of g and A values, confirming the presence of only one chemically equivalent site. The paramagnetic impurity, VO(II), has entered the lattice substitutionally for all the three sites. The superhyperfine structure, in the intensity ratio of 1:4:6:4:1, arising from the protons of the water ligands, has been found in one site. The admixture coefficients have been calculated and the complex is found to be fairly covalent in nature.