Characterization of new-layered Cr(III)-doped chlorocadmiumphosphate, Cd(HPO4)Cl·[H3N(CH2)6NH3]0.5 crystal by EPR and optical studies

Cr(III)-doped Cd(HPO₄)Cl·[H₃N(CH₂)₆NH₃]_0.5, a new-layered cadmium phosphate, is synthesized in acidic condition at room temperature. EPR and optical studies are carried out at room temperature. Polycrystalline EPR spectrum reveals the presence of two sites of Cr(III) ions in this layered phosphate lattice with zero-field splitting values of 24.24 and 7.65 mT, indicating that Cr(III) ions are in distorted octahedral sites. The optical absorption spectrum of the sample indicates near octahedral symmetry for the dopant ions. Crystal field, inter-electronic and bonding parameters are evaluated by collaborating EPR and optical data. The evaluated parameters suggest the mode of entry of Cr(III) ion into the layered phosphate as interstitial site, and bonding between the metal and ligand is partially covalent.     

Exchange interaction and spin dynamics in pentanuclear clusters, Cu3Ln2(ClCH2COO)12(H2O)8 (Ln = Nd3+, Sm3+, Pr3+)

New compounds, [Cu₃Ln₂(ClCH₂COO)₁₂(H₂O)₈]·2H₂O with Ln = Nd³⁺ (I), Sm³⁺ (II), Pr³⁺ (III), built up of pentanuclear clusters were synthesized and studied by means of X-ray analysis and electron paramagnetic resonance (EPR). X-ray data show that all compounds are isostructural and the pentanuclear clusteres may be considered as a linear system with alternating Cu(II) and Ln(III) ions: Cu(2)-L¹-Ln-L²-Cu(1)-L²-Ln-L²-Cu(2) with L¹ and L² being bridging fragments and Cu(1) and Cu(2) being structurally nonequivalent copper complexes. EPR studies demonstrate that in the temperature range of 100–293 K the signals due to only one type of the copper complexes are observed in the spectra of I–III. AtT<100 K the spectral temperature dependence is nontrivial. AtT<30 K new signals are detected in the spectra of I and II. The temperature dependence of the EPR spectra is interpreted under the assumption that the parameter of the exchange interaction Cu(2)-Ln considerably exceeds the parameter of the interaction Cu(1)-Ln. EPR spectra are calculated for the fragments of five paramagnetic centers in the frames of the model taking into account the nonequivalence of two copper complexes, short longitudinal and transverse paramagnetic relaxation times of the rare-earth ions at room temperature and the change of the relaxation rates when the temperature decreases. The results of the calculations show that it is possible to obtain information about the interactions in the system on the basis of the analysis of the temperature dependence of the EPR spectra of the central copper complex. The parameter of the isotropic part of the exchange interaction between copper and neodymium ions (for the interaction Cu(2)-Nd) is estimated as about 15 cm⁻¹. A considerable rearrangement of the spin states when the temperature changes is found for all complexes.     

Investigations of the optical and EPR spectra for (NiX6) (X=Cl, Br, I) clusters

In this paper, the formulae of optical spectral levels and electron paramagnetic resonance (EPR) spectra in trigonal symmetry of 3d⁸ ions are established on the basis of strong field mechanism and a two spin-coupling (SO) parameters model. Unlike the classical crystal-field approach which has only taken the SO coupling of the central metal ions into account, the contribution of the SO coupling of the ligand ions to the optical and EPR spectra has been included in these formulae. When the optical and EPR spectra of the strong covalent crystals are calculated, the reasonable results can be obtained if the two SO parameters model has been put into action. As an application, the optical and EPR spectra of the (NiX₆)⁴⁻ clusters in CsMgX₃:Ni²⁺ (X=Cl, Br, I) crystals have been studied by the complete diagonalization (of energy matrix) method (CDM). The calculated results agree well with experimental findings. From the investigations, a more valid method to calculate the optical and EPR spectra for 3d⁸ ions clusters is provided.     

Growth and EPR properties of KSm(WO4)2 and KEr(WO4)2 single crystals

Growth conditions and electron paramagnetic resonance investigations of two well oriented KSm(WO₄)₂ and KEr(WO₄)₂ single crystals have been presented and discussed. Hyperfine structure of Sm³⁺ ion was detected and analyzed for angular and temperature dependences. EPR spectra of KEr(WO₄)₂ and its angular dependence showed the presence of 5 magnetically nonequivalent Er centers in the crystal. A change in the type of magnetic interactions was analyzed using mixed (Gaussian and Lorentzian) fits of the EPR spectra.     

Calix Receptor Edifice; Scrupulous Turn Off Fluorescent Sensor for Fe(III), Co(II) and Cu(II)

Novel Supramolecular fluorescence receptor derived from calix-system i.e. calix[4]resorcinarene bearing dansylchloride as fluorophore was designed and synthesized. The compound was purified by column chromatography and characterized by elemental analysis, NMR and Mass spectroscopy. Tetradansylated calix[4] resorcinarene (TDCR) shows a boat conformation with C₂v symmetry. The complexation behaviour of metal cations [Ag(I), Cd(II), Co(II), Fe(III), Hg(II), Cu(II), Pb(II), Zn(II), U(VI) (1?×?10^-4?M)] with tetra dansylated calix[4]resorcinarene (1?×?10^-6?M) was studied by spectophotometry and spectrofluorometry. Red shift in the absorption spectra led us to conclude that there is strong complexation Fe(III), Co(II) and Cu(II) with TDCR. These metal cations also produce quenching with red shifts in the emission spectra. The maximum quenching in emission intensity was observed in the case of Fe(III) and its binding constant was also found to be significantly higher than that of Co(II) and Cu(II). Quantum yield of metal complexes of Fe(III) was found to be lower in comparison with Co(II) and Cu(II) complexes. Stern Volmer analysis indicates that the mechanism of fluorescence quenching is either purely dynamic, or purely static.     

Synthesis, crystal structure, Cu doped EPR, thermal and voltammetric studies of [Ni(isonicotinamide)2(H2O)4]·(sac)2 single crystal

The single crystal of [Ni(ina)₂(H₂O)₄]·(sac)₂, (NINS), (ina is isonicotinamide and sac is saccharinate) complex has been prepared and its structural, spectroscopic and thermal properties have been determined. The title complex crystallizes in monoclinic system with space group P2₁/c, Z=2. The octahedral Ni(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate ina ligands through the ring nitrogen and four aqua ligands to form discrete [Ni(ina)₂(H₂O)₄] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bands. The magnetic environment of copper(II) doped NINS crystal has also been identified by electron paramagnetic resonance (EPR) technique. The g and A values of Cu²⁺ doped NINS single crystal were calculated from the EPR spectra recorded in three mutually perpendicular planes. These values indicated that the paramagnetic centre has a rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The complex exhibits only metal centred electroactivity in the potential range of −2.00, 1.25 V versus Ag/AgCl reference electrode.     

Co (III) ions high-spin configuration in nonstoichiometric Co3O4 films

Optical spectra in UV, visible and near IR wave-length range have been measured and the SCF X_∝SW method calculation of Co₃O₄ electronic structure has been carried out. The nature of absorption bands observed has been revealed. As shown, the principal peculiarity of the nonstoichiometric films electronic structure compared with “bulk” samples is a stabilization of Co(III) ions high-spin configuration in Co₃O₄ spinel octahedral sublattice.     

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.     

Stereochemistry of New Nitrogen Containing Heterocyclic Aldehydes. II. Novel Bis-Bidentate Azodye Compounds

A novel family of chelating bis-bidentate azodye compounds¹ with Cu(II), Co(II), Ni(II), Fe(II), Hg(II), Pd(II), UO₂(II), Fe(III), Cr(III), La(III), Ru(III) and Zr(IV) has been prepared and characterized on the basis of analytical, magnetic, ¹H and ¹³C NMR, EPR and electronic spectral studies. Tentative structures for the polymeric complexes are proposed. The important IR bands and the main ¹H and ¹³C signals are assigned and discussed relative to the molecular structure. Various EPR parameters for Cμ(II), have been calculated. The ligand acts as a dibasic bis-bidentate chelating agent coordinating through CO, N=N, COOH and OH groups by replacement of a proton from the two latter groups. Considerable interest has also been focused on the synthesis of the azo compound and its polymeric metal complex due to its wide potential applications. The thermal decomposition behavior of the complexes is also discussed.     

Strontium Tetraborate Glasses Doped with Transition Metal Ions: EPR and Optical Absorption Study

Electron paramagnetic resonance (EPR) and optical studies have been carried out on Cu(II)-, VO(II)- and Cr(III)-doped strontium tetraborate glasses to understand the distortion and substitution of these ions. The EPR results of Cu(II) glass indicate that g _∥ > g _⊥, typical for the tetragonally elongated octahedral site of the Cu(II) impurity. The evaluated covalency parameter 0.788 suggests a moderate covalency for the bonding. By correlating EPR and optical results, the in-plane π-bonding β₁ ² is evaluated as 0.715. In the vanadium-doped glasses, the distortion must be a tetragonally elongated octahedron, similar to Cu(II). However, the EPR studies show that g _⊥ > g _∥ indicating the tetragonally compressed octahedral site for the ion. The site symmetry is C _4V. Supported by the optical absorption, evaluated parameters propose a moderate covalency. The EPR and optical results for Cr(III) glass indicate the distorted octahedral site symmetry in the host lattice. These results further suggest that the bonding between Cr(III) and the ligands is covalent. Authors' address: Renduchintala V. S. S. N. Ravikumar, Department of Physics, Acharya Nagarjuna University, Nagarjuna Nagar 522510, India     

EPR investigation of the spin-spin interactions in a Cu(II)-Gd(III)-Fe(III) heterospin system

The spin-spin interactions in a system that contains three different spin carriers, [{LCu}Gd(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O (1) [L²⁻, N,N-propylenedi(3-methoxysalicylideneiminato)], were investigated by electron paramagnetic resonance spectroscopy. Additional information was obtained by analyzing the discrete heterobinuclear system [LCu(OH₂)Gd(O₂NO)₃] (2), which contains the Cu(II)-Gd(III) pair also existing in the structure of 1, and the compounds [{LCu}Gd(H₂O)₃{Co(CN)₆}] _n ·3.5nH₂O and [{LCu}La(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O, which are isostructural with 1 and in which the paramagnetic low-spin Fe(III) and Gd(III) ions were replaced by diamagnetic low-spin Co(III) and La(III), respectively. The investigations were carried out in the temperature range of 293–4 K in both X- and Q-bands and also using a dual-mode X-band. The experimental spectra of the Cu(II)-Gd(III) pairs in 2 were interpreted as the sum of spectra of the ground spin state with total S = 4 and the excited state with S = 3 appearing due to the ferromagnetic exchange interaction between Cu(II) and Gd(III) ions. By fitting the experimental and simulated spectra, the zero-field splitting parameters of the Gd(III) ion are estimated and it is shown that no influence of the anisotropic interaction is detected. The magnetic properties of 1 are discussed from the perspective of the interaction of the Cu(II)-Gd(III) binuclear fragments with the Fe(III) ions.     

Magnetic properties and EPR spectra of [Cu(L-arginine)2](NO3)2·3H2O

Magnetic and EPR data have been collected for complex [Cu(L-Arg)₂](NO₃)₂·3H₂O (Arg=arginine). Magnetic susceptibility χ in the temperature range 2-160 K, and a magnetization isotherm at T=2.29(1) K with magnetic fields between 0 and 9 T were measured. The observed variation of χT with T indicates predominant antiferromagnetic interactions between Cu(II) ions coupled in 1D chains along the b axis. Fitting a molecular field model to the susceptibility data allows to evaluate g=2.10(1) for the average g-factor and J=−0.42(6) cm⁻¹ for the nearest neighbor exchange coupling (defined as H_ex=-∑J_ijS_i·S_j). This coupling is assigned to syn-anti equatorial-apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682 Å, with a total bond length of 6.989 Å and is consistent with the magnetization isotherm results. It is discussed and compared with couplings observed in other compounds with similar exchange bridges. EPR spectra at 9.77 were obtained in powder samples and at 9.77 and at 34.1 GHz in the three orthogonal planes of single crystals. At both microwave frequencies, and for all magnetic field orientations a single signal arising from the collapse due to exchange interaction of resonances corresponding to two rotated Cu(II) sites is observed. From the EPR results the molecular g-tensors corresponding to the two copper sites in the unit cell were evaluated, allowing an estimated lower limit |J |>0.1 cm⁻¹ for the exchange interaction between Cu(II) neighbors, consistent with the magnetic measurements. The observed angular variation of the line width is attributed to dipolar coupling between Cu(II) ions in the lattice.     

X-ray diffraction,differential scanning calorimetric and spectroscopic studies of phase transitions in the bidimensional compound (C12H25NH3)2CdCl4

The existence of three main crystalline phases (called III, II and I) in (C₁₂H₂₅NH₃)₂CdCl₄ has been revealed by differential scanning calorimetry. X-ray diffraction and spectroscopic studies. The crystal- lographic evolution with increasing temperature appears to be monoclinic (III) → orthorhombic (II) → tetragonal (I). The low temperature phase III is the only ordered structure. The phase transition (III-II), which is of first order type, corresponds to an order-disorder mechanism involving the organic part of the structure (alkylammonium chains) whereas the phase transition (II-I), which is of second-order type, is related to the arrangement of the mineral matrix (octahedra of perovskite layers). An intermediate disordered form II', stable in a very narrow temperature range and structurally similar to the form II, has also been observed, so that the transformation (III-II) proceeds, in fact, in two steps (III-II'-II). The variation enthalpies observed at the transitions (III-II'-II) and analyzed through an order-disorder mechanism demonstrate the high disorder of the alkylammonium chains in form II, in agreement with spectroscopic results. No thermal anomaly or spectroscopic modification is observed for the high temperature transition (II-I).     

Electron paramagnetic resonance investigation of K3H(SO4)2 proton conductor doped with Cr ion

The proton arrangement around SO₄ units in K₃H(SO₄)₂ (KHS) was studied in detail by X-band CW EPR spectra of CrO₄³⁻ paramagnetic centre incorporated into KHS during the crystal growth process. The EPR data prove the theoretical model of coherent motion of protons and SO₄ units at the fast-proton conducting phase proposed by Ito and Kamimura.     

A review of spin Hamiltonians applicable to exchange-coupled systems of interest in biomaterials

Dinuclear and tetranuclear complexes of spin-coupled manganese-manganese, manganese-iron, and iron-iron ions occur in enzymes which are of importance in biology and photosynthesis. These multinuclear systems contain higher oxidation states of manganese and iron ions than those of the commonly occurring Mn(II) and Fe(III) mononuclear ions, in which there has been a lot of interest recently with regard to their electron paramagnetic resonance (EPR) spectra. In order to aid the interpretation of EPR spectra, the spin Hamiltonians, and the resulting energy levels, characterizing binuclear and tetranuclear manganese ions will be discussed in this presentation. These will include, in particular, Mn(II)?Mn(III), Mn(III)?Mn(IV), and Mn(IV)?Mn(V) systems for the binuclear situation, and the Mn₄O₂ “butterfly”, cubane, dimer of dimer systems, and diamond structure for the tetramer situation. These coupled systems are characterized by a variety of exchange interactions whose magnitudes and nature, ferromagnetic or antiferromagnetic, affect profoundly the energy levels. In addition, the hyperfine interactions amongst the various⁵⁵Mn nuclei produce a complex EPR spectrum consisting of a large number of hyperfine lines. In order to interpret EPR spectra properly, one needs to simulate them as accurately as possible. Details of a rigorous technique for the simulation of EPR spectra of these systems with matrix diagonalization and homotopy technique will be provided.     

Structural information from EPR powder spectra of Mn(II)-doped Rb2MgCl4, Rb2MgCl3Br and Rb2MgCl2Br2

The structure of the compounds Rb₂MgCl₄, Rb₂MgCl₃Br and Rb₂MgCl₂Br₂ has been determined to be the tetragonal K₂NiF₄ structure. EPR spectra at X and Q-band frequencies of the polycrystalline samples of the Mn(II)-doped compounds, indicate that the Br^? ions prefer to order at special sites of the structure, as concluded from the fact that only octahedral groups [MgCl₆] and tetragonal groups [MgCl₄Br₂] are found.     

Pressure-induced ferroelectricity in {N(CH3)4}2FeCl4

The hydrostatic pressure effect on the stability of phases I, II, III and IV in {N(CH₃)₄}₂FeCl₄ was studied by dielectric and DTA measurements in the temperature and pressure region of -40-30°C and 0–2 kbar. The pressure-induced new phase V found at applied pressures between 0.3 and 1.0 kbar was confirmed to be ferroelectric by the observation of D-E hysteresis loop. These results are compared with those of {N(CH₃)₄}₂XCl₄ (X: Co, Zn and Mn) in this paper.     

EPR and optical absorption studies of VO doped l-alanine (C3H7NO2) single crystals

VO²⁺ doped l-alanine (C₃H₇NO₂) single crystals and powders are examined by electron paramagnetic resonance (EPR) and optical absorption spectroscopy. Three magnetically different sites are resolved from angular variations of l-alanine single crystal EPR spectra. In some specific orientations each VO²⁺ line splits into three superhyperfine lines with intensities of 1:2:1 and maximum splitting value of 2.23 mT. The local symmetries of VO²⁺ complex sites are nearly axial. The optical absorption spectra show three bands. Spin Hamiltonian parameters are measured and molecular orbital coefficients are calculated by correlating EPR and optical absorption data for the central vanadyl ion.     

Spectroscopic studies on Pb3O4-ZnO-P2O5 glasses doped with transition metal ions

Optical absorption, Electron Paramagnetic Resonance (EPR) studies are carried out on lead zinc phosphate glass systems doped with Cr³⁺ and VO²⁺. From optical absorption investigations the crystal-field parameters Dq, B and C are evaluated. EPR measurements on Cr³⁺ systems indicate that Cr³⁺ ions are located at sites with low symmetry. EPR spectra of vanadyl doped system revealed the characteristic nature of vanadyl ion. Spin-Hamiltonian and hyperfine values are evaluated for both the systems. Optical absorption spectra of vanadyl doped system revealed three bands that are characteristic of VO(II) ion in tetragonally distorted octahedral site. By correlating both EPR and optical data, the dipolar coupling constant (P) and Fermi-constant coupling parameter (κ) and molecular orbital coefficients β^?2, e_π^?2 are evaluated. Electron Paramagnetic Resonance and optical absorption studies showed that the chemical bonds of Cr³⁺ ions and VO²⁺ ions with the ligands have more covalent nature. From these studies it is also observed that lead spinals are playing major key role in sustaining the covalent nature of bonding.