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Abstract: Single crystal EPR studies of Mn(II) doped hexaaquazincdiaquabis(malonato) zincate [Zn(H2O)6][Zn(mal)2(H2O)2] have been carried out at room temperature using X-band spectrometer to identify the location of the dopant. Single crystal rotations along the three orthogonal axes show more than 30 line pattern EPR spectra indicating the presence of two types of dopant ions in the host lattice, with intensity ratio of 6:1. However, the latter could not be followed due to its low intensity during crystal rotations. The spin-Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations are: gxx =1.972, gyy =2.000, gzz =2.023, Axx =8.95, Ayy =9.48, Azz =9.93mT, Dxx =−34.49, Dyy =−3.26, Dzz =37.74mT and E =15.6mT. The direction cosines of one of the principal values of g match with that of Zn–O bond in the host lattice, suggesting that the Mn(II) ion entered the lattice substitutionally. The large value of E is indicative of low symmetry of the substitutional site, in accordance with the crystal structure of the isomorphous [Zn(H2O)6][Cu(mal)2(H2O)2]. Covalency of Mn–O bond, estimated from Matamura’s plot, is 9%. Various admixture coefficients, bonding and optical parameters have also been calculated. [Copyright &y& Elsevier]

Abstract: Electron paramagnetic resonance (EPR) study of Cu2+ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu2+ (I), g x =2.1577±0.0002, g y =2.2018±0.0002, g z =2.3259±0.0002, A x =(87±2)×10−4 cm−1, A y =(107±2)×10−4 cm−1, A z =(141±2)×10−4 cm−1; Cu 2+ (II), g x =2.1108±0.0002, g y =2.1622±0.0002, g z =2.2971±0.0002, A x =(69±2)×10−4 cm−1, A y =(117±2)×10−4 cm−1and A z =(134±2)×10−4 cm−1. The ground state wave function of the Cu2+ ion in this lattice is evaluated to be predominantly |x 2 − y 2 :italic>g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex is discussed. [Copyright &y& Elsevier]

Abstract: X-Band electron paramagnetic resonance (EPR) studies of Gd3+ ions in ammonium hydrogen malonate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of four physically equivalent but magnetically inequivalent sites. The zero-field splitting parameters and g factor are determined. The Gd3+ ion is in 8S state; its levels are split by the action of the crystalline electric field of monoclinic symmetry. The optical absorption spectra of Gd3+ ions in single crystals of ammonium hydrogen malonate are also recorded at room temperature. The energy levels of the 4f7 configuration are calculated and compared with those observed experimentally. The values of E 1=5854±11, E 2=31±0.36, E 3=592±3.3 and ζ4f=1595±25cm−1 are found to give the best over-all agreement between experimentally observed and calculated levels. [Copyright &y& Elsevier]

Abstract: Electron paramagnetic resonance (EPR) study of VO2+ doped zinc potassium phosphate hexahydrate single crystal is carried out. The angular variation of the spectra is studied in the three crystallographic planes. The principal value of spin Hamiltonian parameters g and A and the direction cosines which principal axes make with the crystallographic axes are determined. The observed values are site I: g ∥=1.9664±0.0002, g ⊥=1.9973±0.0002, A ∥=150±2×10−4, A ⊥=60±2×10−4 cm−1; site II: g ∥=1.9276±0.0002, g ⊥=1.9921±0.0002, A ∥=155±2×10−4 and A ⊥=62±2×10−4 cm−1. By comparison of direction cosines of g from EPR with the direction cosines of different bonds obtained from crystal structure data it is ascertained that the VO2+ ion occupies Zn2+ substitutional sites. The optical absorption study of the crystal at room temperature is also carried out. The bands observed in the optical absorption spectrum are attributed to d–d transitions. The EPR results together with the optical data are employed to estimate the molecular orbital (MO) coefficients. These MO coefficients (also called bonding coefficients) are further used to discuss the nature of bonding of VO2+ ion with different ligands in the crystal. [Copyright &y& Elsevier]

Abstract: Electron paramagnetic resonance (EPR) and optical absorption studies of VO2+ doped lithium potassium sulphate single crystals are carried out at room temperature. The angular variation of the spectra is studied in the crystallographic a*b, bc and ca* plane. Vanadyl is found to have fixed orientations in the lattice and there are two magnetically inequivalent complexes in the lattice. The spin Hamiltonian parameters obtained from single crystal data for the two sites are, Site I: gxx =2.0015±0.0002, gyy =1.9835±0.0002, gzz =1.9211±0.0002, Axx =(48±2)×10−4 cm−1, Ayy =(64±2)×10−4 cm−1, Azz =(169±2)×10−4 cm−1, Site II: gxx =2.0019±0.0002, gyy =1.9796±0.0002, g zz =1.9225±0.0002, Axx =(48±2)×10−4 cm−1, Ayy =(83±2)×10−4 cm−1, Azz =(178±2)×10−4 cm−1. The first three bands observed in optical absorption spectrum are attributed to d–d transitions and the last band is probably charge transfer band. The band positions are calculated using energy expressions and compared with the observed values to confirm the transitions. Crystal field parameter (D q) and tetragonal parameters (D s and D t) are also evaluated. Using EPR and optical results, the molecular orbital parameters of VO2+ ions in the lattice are evaluated with a tetragonal symmetry approximation (because the rhombic part is small) and the nature of bonding in the complex is discussed. [Copyright &y& Elsevier]

Abstract: X-band electron paramagnetic resonance (EPR) studies of VO2+ ions in sodium citrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO2+ sites. Both the vanadyl complexes are found to take up substitutional position. The angular variation of the EPR spectra in three planes ba*, bc and ca* are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, Site I: g x =1.9680, g y =2.0053, g z =1.9124, A x =79, A y =76, A z =185; Site II: g x =1.9650, g y =2.0067, g z =1.9418, A x =78, A y =70, A z =186×10−4 cm−1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed. [Copyright &y& Elsevier]

Abstract: X-Band electron paramagnetic resonance (EPR) studies of VO2+ ions in l-asparagine monohydrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO2+ sites. Both the vanadyl complexes are found to take up interstitial position. The angular variation of the EPR spectra in three planes ab, bc and ca are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, site I: g x =1.9633, g y =2.0274, g z =1.9797, A x =88, A y =61, A z =161×10−4 cm−1; site II: g x =1.9627, g y =1.9880, g z =1.9425, A x =90, A y =66, A z =167×10−4 cm−1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed. [Copyright &y& Elsevier]

Abstract: EPR study of Cr3+-doped ammonium lithium sulphate single crystals is carried out at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The spin Hamiltonian parameters are found to be g=2.0003±0.0002, D=(269±2)×10−4 cm−1 and E=(82±2)×10−4 cm−1 for site I and g=1.9904±0.0002, D=(251±2)×10−4 cm−1 and E=(79±2)×10−4 cm−1 for site II, respectively. EPR data indicate that the site symmetry of Cr3+ ion in the crystal is distorted octahedron and it enters the lattice substitutionally replacing sites and bind to the neighbouring extra Li+ vacancies necessary for charge compensation. From optical study, the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=908, C=3553, Dq=1974cm−1, h=0.052 and k=0.21. [Copyright &y& Elsevier]

Abstract: Studies of fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn2+: tetramethylammoniumtetrachlorozincate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements were done at liquid nitrogen temperature (77K). The Mn2+ spin Hamiltonian parameters are evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field. The values of the zero field parameters that give good fit to the observed EPR spectra are obtained. The values of different parameters are: g =1.9834±0.0002, =(105±2)×10−4 cm−1, =(100±2)×10−4 cm−1, D =(349±2)×10−4 cm−1, E =(106±2)×10−4 cm−1 and a =(21±1)×10−4 cm−1. The percentage of covalency of the metal–ligand bond has also been determined. From the optical absorption study, the lattice distortion is suggested. The observed bands are assigned as transitions from the 6A1g(S) ground state to various excited quartet levels of Mn2+ ion in a cubic crystalline field. The electron repulsion parameters (B and C) and crystal field parameters (D q and α) providing a good fit to the observed optical spectra are evaluated and the values are: B =737cm−1, C =2322cm−1, D q =670cm−1 and α =76cm−1. The considerable decrease in the values of B and C parameters from free ion values (B =960cm−1, C =3325cm−1) has indicated that there exists a fair amount of covalent bonding between the central metal ion and the ligand. On the basis of deviations Δg = g −2.0023 it has been ascertained whether electrons are transferred to or from the central ion by the action of bonding. [Copyright &y& Elsevier]

Abstract: EPR study of Cr3+-doped tetramethyl cadmium chloride (TMCC) single crystals is carried out at room temperature. The crystal field and spin-Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The g and D parameter values are found to be g=1.9741±0.0002 and D=553±2×10−4 cm−1, respectively. EPR data indicate that the site symmetry of Cr3+ ion in the crystal is distorted octahedron. Cr3+ ions enter the lattice substitutionally replacing Cd2+ sites and bind to the neighboring extra Cd vacancies necessary for charge compensation. The optical absorption spectra are measured in 195–925nm wavelength range at room temperature. From optical study the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=722, C=2845, Dq=2043cm−1, h=1.015 and k=0.21. [Copyright &y& Elsevier]

Abstract: Optical and EPR investigations of chromium and nickel doped zinc phosphate glasses are carried out at room temperature to evaluate crystal field, spin-Hamiltonian and bonding parameters. For Cr3+ ion, the site symmetry is ascribed to a distorted octahedron, whereas the Ni2+ ion is located in a near octahedral site. In addition, the bonding parameters suggest covalent nature for Cr3+ and a moderate covalent nature for Ni2+ in the zinc phosphate glasses. [Copyright &y& Elsevier]