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: g_xx=1.981, g_yy=1.971, g_zz=1.939; A_xx=7.43, A_yy=7.70, A_zz=18.7; site II: g_xx=1.973, g_yy=1.966, g_zz=1.939; A_xx=7.08, A_yy=7.22, A_zz=18.5; site III: g_xx=1.978, g_yy=1.977, g_zz=1.951; A_xx=7.11, A_yy=7.32, A_zz=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.     

Structural elucidation of Cu(II) ion doped in hexaaquozincdiaquobis(malonato)zincate host by EPR spectroscopy

In order to understand the structural behaviour of Cu(II) in a variety of ligand environments, single crystal electron paramagnetic resonance studies of Cu(II) doped in hexaaquazincdiaquabis(malonato)zincate [Zn(H₂O)₆][Zn(mal)₂(H₂O)₂] are carried out at 300 K. Angular variation of copper hyperfine lines in three orthogonal planes shows the presence of single site, with spin Hamiltonian parameters as g_xx=2.034, g_yy=2.159, g_zz=2.388, A_xx=3.39 mT, A_yy=4.89 mT and A_zz=13.72 mT. The g/A tensor direction cosines are compared with various Zn-O directions in the host lattice, which confirm that Cu(II) enters substitutionally in the lattice. The low value of A_zz has been explained by considering admixture of d_²x−²y ground state with d_²z excited state. EPR powder spectra at 300 and 77 K give identical spin Hamiltonian parameters (g_∥=2.367, g_⊥=2.088, A_∥=11.47 mT, A_⊥=2.63 mT). IR, UV-vis and powder XRD data confirm the structure and symmetry of the Cu(II) ion in the host lattice.     

EPR and optical investigation of VO(II) in Zn(C3H3O4)2(H2O)2 single crystals: An interstitial site

EPR spectroscopic investigations on single crystals of diaquabis[malonato(1-)-κ²O,O′] zinc(II) doped with VO(II) ion have been carried out at X-band frequencies and at 300 K. The single crystal, rotated along the three mutually orthogonally axes, has yielded spin-Hamiltonian parameters g and A as: g_xx=1.980, g_yy=1.972, g_zz=1.937 and A_xx=8.4, A_yy=6.1, A_zz=18.1 mT, respectively. These spin-Hamiltonian parameters reflect a slight deviation from axial symmetry to rhombic, which is elucidated by the interstitial occupation of vanadyl ions. The isofrequency plots and powder EPR spectrum have been simulated. The percentage of metal-oxygen bond has been estimated. The optical absorption spectrum exhibits four bands at 257, 592, 720 and 764 nm suggesting a C_4v symmetry. The admixture coefficients and bonding parameters have also been calculated by collaborating EPR data with optical data.     

Effect of paramagnetic doping on an inorganic polymer triaquadipotassiumbis(malonato)zincate: spectroscopic investigation

Spectroscopic investigations on Mn(II)-doped triaquadipotassiumbis(malonato)zincate [K₂(H₂O)₃] [Zn(mal)₂], an inorganic polymer, have been carried out at room temperature using single crystal electron paramagnetic resonance (EPR), ultraviolet–visible, FT-IR and powder XRD techniques. Single crystal rotations along the three orthogonal axes show more than 30 lines of patterns in EPR spectra, indicating the presence of two sites, one with a large D value and the other with a smaller D value. The calculated spin-Hamiltonian parameters are as follows. Site 1: g _xx =2.099, g _yy =2.092, g _zz =1.988, A _xx =9.77, A _yy =9.71, A _zz =8.96 mT, D _xx =?29.09, D _yy =?11.90, D _zz =40.99 mT; Site 2: g _xx =2.040, g _yy =1.995, g _zz =1.924, A _xx =9.51, A _yy =9.09, A _zz =8.80 mT, D _xx =?11.94, D _yy =?7.51 and D _zz =19.45 mT. The direction cosines of g/A/D do not match with the direction cosines of Zn–O bonds in the host lattice for either site, suggesting that both the Mn(II) sites entered the lattice interstitially. Optical results indicate a strong covalent bonding between the metal ion and ligands, with site symmetry being primarily octahedral. The FT-IR and powder XRD data confirm the retention of the crystal structure, even after incorporating a paramagnetic probe. Various admixture coefficients, bonding and optical parameters have also been calculated.     

Single-crystal EPR investigation of Mn(II)-doped biomineral cobalt ammonium phosphate hexahydrate: a case of multiple substitutions

Single-crystal electron paramagnetic resonance (EPR) study of Mn(II)-doped cobalt ammonium phosphate hexahydrate has been carried out at room temperature. The impurity shows more than 30 line pattern EPR spectra along the three crystallographic axes, suggesting the existence of more than one type of impurity ion in the host lattice. The spin Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations, are: site 1: g _xx =1.989, g _yy =1.994, g _zz =1.999; A _xx =?8.97, A _yy =?9.52, A _zz =?9.71 mT; D _xx =?8.09 mT, D _yy =?6.05 mT, D _zz =14.14 mT; site 2: g _xx =1.988, g _yy =2.009, g _zz =2.019; A _xx =?9.11 mT, A _yy =?9.58 mT, A _zz =?9.93 mT; D _xx =?6.61 mT, D _yy =?6.11 mT, D _zz =12.72 mT. The angular variation studies further reveal that the Mn(II) impurities enter the lattice substitutionally. The other Mn(II) sites which are at interstitial locations are difficult to follow due to their low intensity. The variation of zero-field splitting parameter with temperature indicates no phase transition. The observation of well-resolved Mn(II) spectrum at room temperature has been interpreted in terms of ‘host spin-lattice relaxation narrowing’ mechanism.     

Observation of a Substitutional Location for VO(II) in Hexaaquazinc(diaquabismalonato)zincate in Different Crystals,in Addition to Interstitial: An Unusual Observation

Single-crystal electron paramagnetic resonance (EPR) studies of VO(II) doped in hexaaquazinc(diaquabismalonto)zincate have indicated interstitial location for vanadyl, which was a rare observation, considering the structure of the host lattice (K. Arun Prasath Lingam, S. Mithira and P. Sambasiva Rao, Appl. Magn. Reson. 38:295, 2010). However, substitutional location is noticed in a different crystal, in which interstitial resonances are almost absent. Generally, both types of resonances will be noticed in the same crystal. The spin Hamiltonian parameters calculated from the EPR spectra for substitutional location are: g _xx  = 1.981, g _yy  = 1.976, g _zz  = 1.941, A _xx  = 7.96 mT, A _yy  = 6.09 mT, and A _zz  = 17.83 mT. Crystal-field parameters, admixture and molecular orbital coefficients have been calculated from optical data, which reveal a moderately covalent metal–ligand bonding.     

Single crystal EPR studies of Mn(II) doped into zinc ammonium phosphate hexahydrate (ZnNH4PO4·6H2O): A case of interstitial site for bio-mineral analogue

Single crystal EPR studies of Mn(II)-doped zinc ammonium phosphate hexahydrate (ZnNH₄PC₄·6H₂O) have been reinvestigated at room temperature. Single crystal rotations along the three orthogonal axes indicate that the spin Hamiltonian parameters for the interstitial site are:g _xx = 1.966,g _yy = 1.972,g _zz = 1.976;D _xx = -12.28 mT,D _yy = -2.09 mT andD _zz = 14.37 mT;A _xx = 9.06 mT,A _yy = 9.06 mT andA _zz = 11.09 mT;a = -0.11 mT. These parameters differ considerably from the previous report of Chand and Agarwal and indicate the orthorhombic nature of the paramagnetic impurity. The impurity is found to enter the lattice interstitially, in contrast to earlier prediction of substitutional position. The percentage covalency of the Mn-0 bond has been estimated.     

ESR studies of Cu2+ doped in SrC4H4O6·3H2O single crystals

Electron spin resonance spectra of Cu²⁺ doped in single crystals of strontium tartrate trihydrate grown by a diffusion technique have been investigated at 77K. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. ESR measurements gave the following values for the spin-Hamiltonian parameters. Cu²⁺(I): g_gg = 2.0380, g_yy = 2.1317, g_zz = 2.3918 and A_xx = 26.3 G, A_yy = 56.3 G, A_zz = 110.8 G. Cu²⁺(II): g_xx = 2.0497, g_yy = 2.1297, g_zz = 2.3706 and A_xx = 19.2 G, A_yy = 61.4 G, A_zz = 107.2 G.     

Interstitial Substitution of VO(II) in Hexaaquazinc(diaquabismalonato)zincate: A Rare Observation

Single-crystal electron paramagnetic resonance (EPR) studies of VO(II) doped in hexaaquazinc(diaquabismalonto)zincate have been performed at room temperature. Single-crystal rotations along the three orthogonal axes show the presence of a single site in an interstitial position and the location has been identified from crystal data of the host lattice. The spin-Hamiltonian parameters calculated from EPR spectra are g _xx  = 1.973, g _yy  = 1.972, g _zz  = 1.930, A _xx  = 7.05 mT, A _yy  = 6.85 mT, A _zz  = 18.93 mT. Molecular orbital coefficients β ² = 0.71 and ε ² = 0.62 have been calculated and reveal a moderately covalent metal–ligand bond. Optical and EPR data have been used to obtain crystal field parameters, admixture and molecular orbital coefficients.     

Electron paramagnetic resonance of gamma irradiated [(CH3)4N]InCl4 and [(CH3)4N]2CdCl4 single crystals

Gamma irradiated [(CH₃)₄N]InCl₄ and [(CH₃)₄N]₂CdCl₄ single crystals were investigated by electron paramagnetic resonance at ambient temperature, and it has been found that both compounds indicate the existence of (CH₃)₃N⁺ radicals. The g factors were found to be isotropic, and the hyperfine constant for H atoms was measured as 2.86 mT and is isotropic for this radical in these substances. The hyperfine coupling constant of the N nucleus with the hole in (CH₃)₃N⁺ in [(CH₃)₄N]InCl₄ was found to be anisotropic with the A_zz=2.92, A_yy=1.62 and A_xx=1.40 mT. From these, it has been revealed that the C_3v-axis of (CH₃)₃N⁺ radical performs rotational or jumping reorientational motions around a fixed axis, in addition to the rotations of protons in CH₃ groups and the rotational motions of CH₃ groups around the C_3v-axis of the radical. The g, and the hyperfine coupling factors of the N nucleus were isotropic in (CH₃)₃N⁺ in [(CH₃)₄N]₂CdCl₄. This indicates the motional behaviour of the radical in this compound is as in a liquid. This isotropic behaviour of the hyperfine coupling constants was found to be same until the attainable lowest temperature of 113 K in our laboratory.     

Substitutional location for a vanadyl ion in three water coordinated triaqua(1,10-phenanthroline-k2N,N′) (sulfato-kO)magnesium(II) complex: a rare observation

Vanadyl ion substitutes for the central ion, if the doped complex has at least four water molecules. However, the present EPR, XRD, FT-IR and optical absorption studies on vanadyl-doped triaqua(1,10-phenanthroline-k²N,N′)(sulfato-kO)magnesium(II) suggest a substitutional defective nature, which is a rare observation. Single crystal EPR studies in three mutually orthogonal planes indicate two chemically non-equivalent sites with different intensities. However, the lower intensity site could not be analysed due to its weaker intensity and overlap with other sites during crystal rotations. The spin Hamiltonian parameters obtained for the major site are as follows: g _xx =1.973, g _yy =1.972, g _zz =1.930; A _xx =7.15, A _yy =6.77, A _zz =18.92 mT. The direction cosines of principal g and A values suggest that the impurity has entered the lattice substitutionally, which is a very uncommon phenomenon. Admixture coefficients, Fermi contact, dipolar interaction and covalency of metal–ligand bonds have also been evaluated. Optical, FT-IR and powder XRD techniques confirm the structure of the complex.     

A New Paramagnetic Nitrogen Center in Natural Titanium-Containing Diamonds

A new type of nitrogen-related center in natural diamond labeled NU1 is identified as a 〈100〉 split interstitial configuration by means of electron paramagnetic resonance (EPR) and photoluminescence (PL) techniques. In PL this center is seen as an electron-vibration system with a zero-phonon line at 485 nm in the crystals containing S1/OK1 and 440.3 nm/N3 centers. NU1 EPR spectra are described by a spin-Hamiltonian with parameters: S = ½, I = 1 and A _xx (N) = 22.5 G, A _yy (N) = 19.5 G, A _zz (N) = 20.55 G, g _xx  = 2.0043, g _yy  = 2.0032, g _zz  = 2.0020. Directions of A _zz and g _zz coincide and correspond to [001]. The directions of A _xx and A _yy coincide with those of g _xx and g _yy and correspond to [110] and [?110], respectively. Analysis of the phonon structure of the NU1 center suggested that titanium can be the second atom together with nitrogen in the structure of a split interstitial.     

Single crystal EPR investigation on Mn(II) doped biomineral: cobalt potassium phosphate hexahydrate

Single crystal EPR study of Mn(II) doped in cobalt potassium phosphate hexahydrate has been carried out at room temperature. The impurity shows a 30 line pattern EPR spectra along a particular crystallographic axis suggesting the existence of only one type of impurity in place of Co(II) ion in the host lattice. The spin Hamiltonian parameters have been estimated as: g₁₁=2.011, g₂₂=1.998, g₃₃=1.991, and A₁₁=−8.9, A₂₂=−8.8, A₃₃=−8.4 mT and D₁₁=−15.2, D₂₂=−9.4, D₃₃=24.6 mT, respectively. The sign of A is designated as negative and D as positive. The covalency of metal-oxygen bond has been estimated. The relaxation times, calculated as a function of temperature, indicate spin-lattice relaxation narrowing at room temperature.     

Characterisation of the Ru/MgF2 catalyst with adsorbed O2, NO, CO probe molecules by EPR and IR spectroscopy

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst during O₂, NO, and CO adsorption at room temperature on 1 wt% Ru/MgF₂ catalysts prepared from Ru₃(CO)₁₂ . Both EPR and IR results provided clear evidence for the interaction between surface ruthenium and probe molecules. No EPR signals due to ruthenium (Ru) species were recorded at 300 and 77 K after H₂-reduction of the catalyst at 673 K. However, at 4.2 K a very weak EPR spectrum due to low-spin (4d⁵) Ru³⁺ complexes was detected. A weak anisotropic O₂^- radicals signal with g_∣∣=2.017 and g_⊥=2.003 superimposed on a broad (ΔB_pp=120 mT), slightly asymmetric line at g=2.45(1) was identified after O₂ admission to the reduced sample. Adsorption of NO gives only a broad, Gaussian-shaped EPR line at g=2.43(1) indicating that the admission of NO, similarly to O₂ adsorption, brings about an oxidation of Ru species in the course of the NO decomposition reaction. Introduction of NO over the CO preadsorbed catalyst leads to EPR spectrum with parameters g_⊥=1.996, g_∣∣=1.895, and A_⊥^N=2.9 mT assigned to surface NO species associated with Ru ions. The IR spectra recorded after adsorption of NO or CO probe molecules showed the bands in the range of frequency characteristic of ruthenium nitrosyl, nitro, and nitrate/nitrite species and the bands characteristic of ruthenium mono-and multicarbonyls, respectively. Addition of CO after NO admission to the catalyst leads to appearance in the IR spectrum, beside the ones characteristic of NO adsorption, the bands which can be attributed to Ru-CO₂ and Ru-NCO species, indicating that the reaction between NO and CO occurs. These species were also detected after CO adsorption followed by NO adsorption, additionally to the band at 1850 cm⁻¹ being due to cis-type species.     

EPR,FTIR, Powder XRD and Optical Absorption Studies of Cu(II) Ion in Triaqua(1,10-Phenanthroline-k<Superscript>2</Superscript><Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′)(Sulfato-kO)Zinc(II)

Electron paramagnetic resonance (EPR), optical, Fourier-transform infrared (FTIR) and powder X-ray diffraction (XRD) studies have been carried out on Cu(II)-doped triaqua(1,10-phenanthroline-k² N,N′)(sulfato-kO)zinc(II) to get information about the position and spin Hamiltonian parameters of the dopant. Angular variation of copper hyperfine structure lines in EPR study shows the presence of a single site with g and A values as: g _xx  = 2.003, g _yy  = 2.001, g _zz  = 2.223; A _xx  = 4.41 mT, A _yy  = 2.39 mT and A _zz  = 12.16 mT. The slightly lower parallel value obtained for the copper nucleus has been explained by considering admixture of the ground state with the excited state. The direction cosines of principle g and A values suggest that the impurity is present interstitially. Admixture coefficients and additional parameters (P, k, α ², α′) have also been evaluated. Optical, FTIR and powder XRD techniques have been used to reconfirm the structure of the host lattice.     

ESR studies of Cl2- (VK) centre trapped in irradiated Ca(ClO3)2 . 2H2O single crystals

A Cl₂- centre has been trapped in X or γ-irradiated Ca(ClO₃)₂. 2H₂O single crystals at 298 K, when the irradiated crystals were illuminated with ultra-violet light (360 nm). This centre is formed at the expense of ClO₂ centres in this crystal. This Cl₂ ^- centre is trapped at two magnetically inequivalent sites in the crystal lattice and these sites become equivalent when the static magnetic field is parallel or perpendicular to the b axis. At many orientations this centre reveals ‘super-hyperfine’ interaction with a proton (I = 1/2) of the water of crystallization. The magnetic parameters are close to those observed in alkali chlorides and the E.S.R. spectrum has been fitted to an orthorhombic spin hamiltonian. The principal g values are g_xx = 2·035, g_yy = 2·033 and g_zz = 2·000 and those of the A values are A_xx = 15·0, A_yy = 31·0 and A_zz = 109·0 G. The shfs parameters are A _‖' = 5·0 A _⊥' = 1·0 G. The V_K centre trapped in this lattice is exceptionally stable at room temperature.     

EPR studies of Cu2+ in anhydrous sodium oxalate

Electron paramagnetic resonance spectra of Cu²⁺ doped in single crystal of anhydrous sodium oxalate grown by slow evaporation from saturated aqueous solutions have been investigated. EPR measurements gave the following values for the spin Hamiltonian parameters: g_xx = g_yy = 2.0741, g_zz = 2.3253, A_xx = A_yy = ?14.9G and A_zz = ?147.7 G. The principal axes of the hyperfine coupling and g tensors are spatially coincident. Using the optical absorption energy values given for a similar complex we have estimated the values of the bonding parameters and orbital-reduction factors for the system under investigation.     

Single crystal EPR studies of Mn(II) doped zinc sodium sulphate hexahydrate: a case of interstitial substitution

Single crystal Electron Paramagnetic Resonance studies on Mn(II) doped zinc sodium sulphate hexahydrate are carried out at room temperature. The angular variation spectra of the crystal in the three orthogonal planes show that the paramagnetic impurity Mn(II) has entered the host lattice interstitially. The spin Hamiltonian parameters calculated are: g_xx=1.899, g_yy=1.944, g_zz=2.024; and The probable location for the interstitial site has been identified from the position of various atoms in the lattice. The variable temperature study for polycrystalline sample has been carried out, which indicates no phase transition. The percentage covalency of Mn-O bond has been estimated to be 8.5%.     

Single crystal EPR and optical absorption study of Cr doped l-histidine hydrochloride monohydrate

EPR study of the Cr³⁺ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.9108±0.0002, g_y=1.9791±0.0002, g_z=2.0389±0.0002, A_x=(252±2)×10⁻⁴ cm⁻¹, A_y=(254±2)×10⁻⁴ cm⁻¹, A_z=(304±2)×10⁻⁴ cm⁻¹ for site I and D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.8543±0.0002, g_y=1.9897±0.0002, g_z=2.0793±0.0002, A_x=(251±2)×10⁻⁴ cm⁻¹, A_y=(257±2)×10⁻⁴ cm⁻¹, A_z=(309±2)×10⁻⁴ cm⁻¹ for site II, respectively. The optical absorption studies of single crystals are also carried out at room temperature in the wavelength range 195-925 nm. Using EPR and optical data, different bonding parameters are calculated 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: B=636, C=3123, Dq=2039 cm⁻¹, h=1.46 and k=0.21, respectively.     

Exhibition of low hyperfine coupling constant for copper(II) in magnesium rubidium sulphate hexahydrate

Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g₁₁=2.133, g₂₂=2.137, g₃₃=2.327, A₁₁=0.01, A₂₂=1.44 and . The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx²-y² ground state with dz² excited state. Bonding parameters, κ=0.254, , α²=0.706, α=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example.