Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part II: VO(II)--a case of substitutional site

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2 Zn(SO4 )2 ·4H2 O and K2 Zn(SO4 )2 ·6H2 O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂ Zn(SO₄ )₂ ·4H₂ O (DPPH) and K₂ Zn(SO₄ )₂ ·6H₂ O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.

Variable temperature EPR studies of Cu²+ and VO²+ doped potassium dihydrogen citrate (C6H7KO7)

Electron paramagnetic resonance (EPR) studies of single crystals and powder samples of Cu(2+) and VO(2+) doped potassium dihydrogen citrate (PDHC) have been carried out at different temperatures. The temperature-dependant g and A values have been obtained for powder spectra of both Cu(2+) and VO(2+) ions in PDHC and the ground state of Cu(2+) ion has been determined. The powder spectra recorded for Cu(2+) ion in the temperature range 70-298 K are discussed with Jahn-Teller distortion. It is concluded that the g and A values of Cu(2+): PDHC show the static property at low temperatures. For all temperatures, the result g(//)<g(⊥)<g(e) of VO(2+): PDHC indicates that the unpaired electron exists in the d(xy) orbital.

EPR and optical studies of vanadium doped potassium dihydrogen citrate (C6H7KO7) single crystal

An EPR and optical studies of VO2+ doped potassium dihydrogen citrate (PDHC) single crystals have been carried out at room temperature. It crystallizes in triclinic symmetry with the unit cell dimensions: a=11.343Å, b=13.078Å, c=6.272Å, α=89.79°, β=94.36°, γ=104.2°. The angular variation of EPR spectra have shown that two different VO2+ complexes are located in different chemical environments and each environment contains one magnetically VO2+ site occupying substitutional position in the lattice and show very high angular dependence.

EPR studies of VO2+ doped bis(saccharinato)bis(pyridine) zinc (II) single crystals

Electron paramagnetic resonance (EPR) studies of vanadyl ions, VO2+, as paramagnetic impurity in bis(saccharinato)bis(pyridine)zinc (II) [hereafter, Zn(sac)2(py)2] are made at room temperature. The angular variation of the EPR spectra has shown that three different VO2+ complexes are located in different chemical environments and each environment contains two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The spin-Hamiltonian parameters are determined and these parameters have been used to assess the bonding coefficients of the VO2+ ion in [Zn(sac)2(py)2] lattice. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in [Zn(sac)2(py)2] were present in octahedral coordination with a tetragonal compression and belong to C4v symmetry. The parallel and perpendicular components of axially symmetric g and hyperfine tensors are evaluated and the results are discussed.

Single crystal EPR study of VO(II) in magnesium potassium phosphate hexahydrate: a case of two substitutional vanadyl ions

Single crystal EPR study of VO(II)-doped magnesium potassium phosphate hexahydrate has been carried out at room temperature. Single crystal rotations in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice in place of magnesium ions by replacing the equatorial and axial coordinated water molecules. The spin Hamiltonian parameters obtained for the two substitutional sites are: site 1: g1=1.9800, g2=1.9774, g3=1.9296, A1=7.25 mT, A2=8.09 mT, A3=18.69 mT and site 2: g1=1.9802, g2=1.9765, g3=1.9296, A1=6.82 mT, A2=8.48 mT, A3=18.75 mT, respectively. Superhyperfine, from protons of ligand water molecules, has been observed at certain orientations. It has been concluded that VO bond directions of the two substitutional ions are orthogonal to each other.

Single crystal EPR studies of paramagnetic ions doped zinc potassium phosphate hexahydrate; Part III: Mn(II)-a case of rhombic distortion

Single crystal electron paramagnetic resonance (EPR) studies of Mn(II) doped zinc potassium phosphate hexahydrate have been carried out at room temperature. Single crystal rotations along the three orthogonal axes indicate orthorhombic symmetry with spin-Hamiltonian parameters as: g(xx) = 1.9997; g(yy) = 1.9538; g(zz) = 1.9524, D(xx) = 15.49 mT; D(yy) = 0.22 mT; D(zz) = -15.71 mT, A(xx) = 11.70 mT; A(yy) = 10.53 mT; A(zz) = 10.42 mT and a = 0.8 x 10(-4) cm(-1). A large E term indicates considerable distortion from axial symmetry. The impurity is found to enter the lattice substitutionally. The distortion axis for the impurity has been identified along one of the Zn-O bond directions in the crystal.