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

Single crystal electron paramagnetic resonance (EPR) studies were carried at room temperature for VO(II) doped zinc potassium phosphate hexahydrate. The results indicate that the paramagnetic impurity has entered the lattice only substitutionally, as confirmed by the single crystal rotations. The spin Hamiltonian parameters calculated from the spectra are g_//=1.9356, g=1.9764, A_//=200.9 G and A=76.5 G. The optical absorption spectrum exhibits three bands (800, 670 and 340 nm) suggesting the C_4v symmetry and the optical parameters evaluated are Dq=1492, Ds=−3854 and Dt=186 cm⁻¹.     

Single crystal EPR study of VO(II)-doped magnesium potassium Tutton’s salt — Part 4

Single crystal EPR studies of VO(II)-doped magnesium potassium Tutton’s salt have been carried out at room temperature. The results indicate that the paramagnetic impurity has entered the lattice, both substitutionally and interstitially and the maximum hyperfine for the substitutional site along the a axis corresponds to the minimum hyperfine for interstitial site and vice versa. The spin Hamiltonian parameters obtained from single crystal data for these sites are: Site 1, g_||=1.954(1); g=1.998(1), A_||=19.80(2) mT; A=7.61(2) mT; Site 2, g_||=1.997(1); g=1.952(1), A_||=7.66(2) mT; A=19.85(2) mT. Superhyperfine from ligand protons have been observed at certain orientations for Site 2 impurity. Powder spectrum shows a set of eight parallel and perpendicular features indicating the presence of only one site and these values matched with Site 1 values. From these observations, it has been concluded that the two vanadyl impurities are approximately at right angles to each other. Cooling the sample to 77 K does not change the spectra appreciably. The admixture coefficients have been calculated from Site 1 data, which agree well with the reported values.     

Sorption of Cu2+ ions by chitin and chitosan from aqueous solutions. Molecular structure of complexes formed

The sorption of Cu²⁺ ions by chitin and chitosan from aqueous solutions has been investigated, as well as the molecular structure of the complexes formed. The static exchange capacities have been determined, equal to 3.5 and 0.25 mmole/g for chitosan and chitin, respectively, and the partition coefficients (5000 and 70 g/ml). It has been shown that in complex formation a bond with the amino group is formed as the result of the substitution of a proton in the latter. The EPR spectra of these complexes have been obtained and their radiospectroscopic parameters determined (g = 2.334,g = 2.054,A = 0.0156 cm^–1, andB = 0.0028 cm^–1 for chitin, andg = 2.231,g = 2.048,A = 0.0192 cm^–1, andB = 0.0025 cm^–1 for chitosan). For chitosan the ligands are two nitrogen atoms of the amino groups and two oxygen atoms of the hydroxyl groups in the position C³ of adjacent glucosamine rings; for chitin, the oxygen atoms of the acetyl groups take part in addition in the complex formation. The analysis of the radiospectroscopic parameters and their comparison with published data lead to the conclusion that the Cu²⁺ complex with chitosan has a tetragonal symmetry, while the complex with chitin most probably has an octahedral structure.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2305–2311, October, 1992.     

Distorted pentacoordinate copper(II) complexes containing a tridentate ligand

Summary Copper(II) complexes with a tridentate chelating ligand within the general 2N, X (X = O or S) donor class, containing abis(benzimidazolyl) donor set, were prepared and characterized. X-band e.p.r. spectra of the complexes indicateg >g and the largeg and lowA have been interpreted in terms of a distorted basal plane. Superimposed on theg component are five SHF lines withA _N = 16±2G, supporting the interaction of two nitrogen atoms with the copper nucleus. Thus, the basal plane of the complex comprises 2N atoms, with the ligand hetero atom being axially coordinated.     

Synthesis,crystal structure and spectroscopic characterization of a hydrogen-bonded 1D copper(II) complex

Novel 1:2 and 1:1 (M:L) copper(II) complexes have been prepared from the tridentate ligand 2-(1-methyl-2-aza-5-oxapentyl)phenol (H₂L¹). The crystal structure of [Cu(HL¹)₂] (1) exhibits a noncentrosymmetric square-planar geometry with a slightly tetrahedral distortion. The Cu^II atom is coordinated by two amino N and two phenoxo O atoms of two (HL¹)^– ligands. The phenoxo and the alkoxy groups are involved in two strong intramolecular hydrogen bonds. The coordination moieties are further connected to a 1D linear structure by the action of intermolecular hydrogen bonds between the alkoxyl and the amino groups. The importance of steric hindrance introduced by the methyl group in the molecular structure and the packing of the complex molecules has been demonstrated. The e.p.r. parameters of (1) have been obtained: g = 2.231, g = 2.005, g _iso = 2.080, A = 185.0 G, A _iso = 86.5 G, A = (3A _iso – A )/2 = 37.3 G. These results confirm a distorted square planar stereochemistry with a ( )¹ ground state.     

ESR spectra of spacered copper(II) dimers of 5-bromo-2-hydroxyacetophenone acyldihydrazones based on aliphatic dicarboxylic acids

Binuclear copper(II) complexes with 5-bromo-2-hydroxyacetophenone acyldihydrazones (H₄L) with the composition [Cu₂L·nPy] where the coordination polyhedra are linked by polymethylene chains with different lengths (from one to five units) have been synthesized and studied. The ESR spectrum of a polycrystalline sample of a complex based on malonyldihydrazone contains a major signal (g = 2.11) together with a weak signal corresponding to the forbidden transition (ΔM _S = 2, g = 4.18). At room temperature, ESR spectra of solutions of complexes of acyldihydrazones based on malonic, succinic, glutaric, and adipic acids contain seven HFS lines from two equivalent copper nuclei. These lines result from weak spin-spin exchange interaction between two unpaired electrons with the constant (36–38)·10⁻⁴ cm⁻¹. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of a complex of the acyldihydrazone based on pimelic acid contains a signal of four HFS lines (a _Cu = 69.5·10⁻⁴ cm⁻¹), which is common to the monomeric copper(II) compounds. In the parallel orientation, the ESR spectrum of a frozen solution of the complex of malonyldihydrazone contained the superposition of signals due to fine and hyperfine structures with similar constants (D _∥ = 0.0074 cm⁻¹, A _∥ = 0.0070 cm⁻¹, g _∥ = 2.089, g _⊥ = 2.053). __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1752–1757, August, 2005.     

Oxovanadium(IV) complexes of bromo-and methoxy substituted N1,N4-diarylidene-S-methylthiosemicarbazones

Four new oxovanadium(IV) compounds were prepared by template reaction of salicyl-, 5-bromosalicyl-and 3-methoxysalicyl-aldehyde S-methylthiosemicarbazones with 2-hydroxy-, 5-bromo-2-hydroxy-and 3-methoxy-2-hydroxy-benzaldehyde in various combinations. The compounds were isolated as stable solid compounds with general formula [VO(L)] and characterized by elemental analysis, conductivity and magnetic measurements, electronic, IR and EPR spectroscopy. The X-band EPR signals recorded from powder forms of all samples have a single asymmetric line shape and theoretical fit studies proved the presence of axial symmetry around the paramagnetic vanadium ions. The anisotropic Lande splitting factors take values of g_‖ < g_⊥ < g_e = 2.0023. Orbital energy levels for magnetic electrons were determined from theoretically well fitted Spin Hamiltonian parameters. The EPR spectra recorded from solution forms almost have isotropic character.     

Synthesis,characterization and biological analysis of the complex [VO(Hdhp)<Subscript>2</Subscript>] (H<Subscript>2</Subscript>dhp = 2,3-dihydroxypyridine)

A new vanadium (IV) complex with the monoanion of 2,3-dihydroxypyridine (H₂dhp), or 3-hydroxy-2-(1H)-pyridone, was synthesized, characterized by physicochemical techniques and tested biologically. The EPR data for the [VO(Hdhp)₂] complex in DMF are: g _x = 1.9768, g _y = 1.9768 and g _z = 1.9390; A values (10⁻⁴ cm⁻¹): A _x , 59.4; A _y//, 59.4; A _z , 171.0. The νV=O band in the IR spectrum of the complex is at 986 cm⁻¹. The complex is paramagnetic, with μ_eff = 1.65 BM (d¹, spin-only) at 25 °C. The irreversible oxidation process [V(V)/V(IV)] of the [VO(Hdhp)₂] complex, as revealed in a cyclic voltammogram, occurs at 876 mV. The calculated molecular structure of [VO(Hdhp)₂] shows the vanadium(IV) center in a distorted square pyramidal environment, with the oxo ligand in the apical position and the oxygen donor atoms of the Hdhp ligands in the basal positions. The ability of [VO(Hdhp)₂] to mimic insulin, and its toxicity to hepato-biliary functions, were investigated in streptozotocin-induced diabetic rats and it was concluded that the length of treatment and the amount of [VO(Hdhp)₂] administered were effective in reducing experimental diabetes.     

Conformation of perfluoroalkyl radicals in the solid phase

An equilibrium conformation of the perfluoroalkyl ∼CF₂·CF₂ radical at 77 K in matrices of polytetrafluoroethylene andn-perfluoroalkanes was studied. Upon cooling from 300 to 77 K at temperatures below 200 K, the ESR spectrum of this radical changes, and the well-resolved hyperfine structure appears. The hyperfine splitting constants on nuclei of two nonequivalent F_β atoms were determined: 2.2 and 1.1 mT, respectively. TheA _∥ andA _⊥ values for the F_α atoms are 22.5 and 3.3 mT, respectively. The conformational angle between the axis of the orbital of an unpaired electron and projection of the C_β−C_γ bond is 5.6°. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 331–334, February, 1999.     

Coordination chemistry of copper(II) complexes with N4, N4S2, and N4O2 donor macrocyclic ligands: Biological aspects—antifungal, synthesis, spectral studies, and magnetic moments

Three macrocyclic ligands and their complexes with copper(II) salts (with anions Cl⁻, NO ₃ ⁻ , and NCS⁻) were prepared and investigated using a combination of microanalytical analysis, melting point, molar conductance measurement, magnetic susceptibility measurement, and electronic, IR and ESR spectral studies. Ligands L¹, L², and L³ having N₄, N₄O₂, and N₄S₂ core, respectively, and all the donor atoms of these ligands are bonded with Cu, which is confirmed by a seven-line pattern observed at half-field in the frozen (H₂O: MeOH = 10: 1 at pH 10) solution ESR spectrum. The polycrystalline ESR data (g _∥ = 2.20–2.27, g _⊥ = 2.01–2.05, and A _∥ = 120–270) of all the complexes together with the high asymmetry geometry suggest that all complexes appear to be near the static distortion (CuN₄O₂ and CuN₄S₂ chromophore geometry). The electronic spectra of the complexes involve two bands at the same intensity corresponding to a cis-distorted octahedral geometry. A common structural feature of both ligand L² and ligand L³ is that two different donor atoms at five-membered heterocyclic aromatic ring due to this N₄O₂ and N₄S₂ chromophore form stable six-membered chelate rings with metals via these two, Cu-O and Cu-S, new interactions comparatively to the first macrocyclic ligand, which has four-membered N,N′-chelate rings. The cyclic voltammetric studies point to a two-step electron transfer indicating the reduction of the two copper atoms to copper(I), i.e., Cu(III)Cu(II) ⇄ Cu(II)Cu(I) ⇄ Cu(I)Cu(0). The molar conductance for the complexes corresponds to 1: 2 and is nonelectrolyte in nature. The magnetic moment (μ_eff) of the complexes lie in the range between 1.80–1.96 μ_B. Finally, these complexes were screened for their antimicrobial activity against Aspergillus-niger of fungal strains. The text was submitted by the authors in English.     

THE EPR SPECTRUM OF COPPER-DOPED SINGLE CRYSTALS OF GLYCYLGLYCINE

Abstract

The EPR Spectrum of Cu(II)-doped into a single crystal of α-glycylglycine is reported. The results show that there are several magnetically non-equivalent sites, only two of which were strong enough to be analysed. The values parameters in the spin Hamiltonian deduced from the data are: g _z =2.242 ± 0.003, g _x =2.062 ± 0.005, g _y =2.044 ± 0.005, A _z =162.8 ± G, A _x =32.6 ± 2.0 G, A _y =21.6 ± 2.0 G. The Cu(II) environment seems to be square planar and involving four ligand molecules, each molecule forming one bond with the copper. The nitrogens are located in the trans position. The bonding is chiefly in-plane [sgrave]-bonding.     

Carbon monoxide and oxygen interaction with Ru/MgF<Subscript>2</Subscript> catalyst: IR and EPR studies

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst upon the adsorption of CO and O₂ on 1.37 wt% Ru/MgF₂ catalysts derived from Ru₃(CO)₁₂. The presence of Ru ^x+ sites in spite of a reductive H₂ treatment at 673 K was observed by EPR and IR spectroscopy beside metallic Ru⁰ species. Both IR and EPR results provided clear evidence for the interaction between surface ruthenium and probe molecules. The IR spectra recorded after admission of CO showed a band at approx. 2000 cm⁻¹, due to linearly adsorbed CO on Ru⁰/MgF₂ and two bands at higher frequencies (approx. 2140 and approx. 2070 cm⁻¹), related to CO on oxidized Ru ⁿ⁺ species, e.g., to Ru(CO)₃ complex with Ru in the 1+ and/or 2+ state of oxidation and Ru(CO)₂ with Ru in the 3+ and/or 4+ state of oxidation. A weak anisotropic EPR signal with g _‖ = 2.017 and g _⊥ = 2.003 is due to O ₂ ⁻ radicals and a formation of Ru⁴⁺-O ₂ ⁻ complex is postulated. The Ru³⁺ appears to oxidize to Ru⁴⁺ and the resulting dioxygen anion is coordinated to the ruthenium. The strong, isotropic EPR signal at g ₀ = 2.003 detected upon admission of CO is attributed to CO radical anion rather than to any ruthenium carbonyl complexes.     

ESR spectra of trifluoromethyl radical formed during the solid-phase photodecomposition of long-lived perfluoro-2,4-dimethyl-3-ethylpentyl-3 radicals

The products of photolysis of the long-lived radical [(CF₃)₂CF]₂C^·C₂F₅ at 77 K were studied by ESR. The mechanism of photodecomposition to form ^·CF₃ radicals was proposed. The ESR spectra of the trifluoromethyl radicals stabilized at 77 K in a glassy hexafluoropropylene trimer matrix were simulated, and the parameters À = 25.15 mT, À = 9.1 mT, and g = l.9996, g = 2.0056 were determined.     

EPR study of the nature of the impurity centers responsible for the scintillation properties of the Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

The binary molybdate Li₂Zn₂(MoO₄)₃ of a new crystal type was characterized by EPR, optical spectroscopy, and X-ray diffraction methods. The crystals have the Pnma symmetry group and the lattice parameters a = 5.1139(5) Å, b = 10.4926(13) Å, c = 17.6445(22) Å; Z = 4. The crystals possess scintillation properties; emission is caused by the presence of impurity levels in the forbidden band. The EPR studies of the nature of the impurity centers responsible for the scintillation characteristics of the crystal showed that the centers were Cu²⁺ ions substituted for zinc ions in the oxygen octahedra. The directions of the main values of the g and tensors (g _zz , A _zz ) correspond to the direction of O-Cu-O of the oxygen octahedron distorted along the Z axis. The EPR spectra of the copper ions are described by the spin Hamiltonian with the parameters g _‖ = 2.38, g _⊥ = 2.06; A _‖ = 116 G, A _⊥ = 0 G.     

From Planar Toward Tetrahedral Copper(Il) Complexes: Structural and Electron Paramagnetic Resonance Studies of Substituent Steric Effects in an Extended Class of Pyrrolate-Imine Ligands

A series (1a-1h) of crystalline bis-pyrrolate-imine copper(II) complexes was isolated in good yield (typically 60-90%) by reaction of the Schiff base 2-N-(R)-pyrrolecarbaldimine (where R is an alkyl group of variable steric capacity) with a copper(II) salt and base in methanol or water. For new complexes 1f-1h, pyrrolate-imine coordination is inferred by loss of ν(N-H) and a shift (ca. 40 cm^?1) to lower energy for ν(C=N) in the infrared spectra relative to free Schiff base. The X-ray crystal structures of 1f, where R = benzyl, and 1g, where R = diphenylmethyl, show trans geometry of the pyrrolate-imine moieties around Cu(II). The distortion from planarity of the CuN₄ coordination sphere, defined as the dihedral angle between the two chelating N(imine)-Cu-N(pyrrolate) planes, is 33.13(5)° for 1f and 29.3° for 1g. X-band electron paramagnetic resonance (EPR) spectra for 1a-1h in glassy solutions (ca. 100 K) are approximately axial, with an inverse correlation between A _z and g _z . At room temperature in fluid solution there is an inverse correlation between A _iso and g _iso. Plots of A _z , A _iso, g _z , or g _iso as a function of the dihedral angles between the ligand planes in 1f and 1g, as well as the previously characterized 1a (R = H) and 1d (R = tert-butyl) were used to determine the dihedral angles of the four complexes of unknown geometry. A red-shift in the ligand field bands in the electronic absorption spectra in chloroform also correlates with increasing dihedral angle. For each of these correlations, the data point for the diphenylmethyl derivative 1g deviates slightly from the line based on the other complexes; this is attributed to crystal packing forces causing a smaller dihedral angle for 1g in the crystal than in solution.     

Structural elucidation of transition metal complex by single crystal EPR study

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: g_xx = 1.972, g_yy = 2.000, g_zz = 2.023, A_xx = 8.95, A_yy = 9.48, A_zz = 9.93 mT, D_xx = −34.49, D_yy = −3.26, D_zz = 37.74 mT and E = 15.6 mT. 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.     

Electron Paramagnetic Resonance Spectra of PrIons Doped in Sr2SnO4and Ba2SnO4

The isotropic electron paramagnetic resonance (EPR) spectra of powders with Pr⁴⁺doped inM₂SnO₄(M=Sr, Ba) with K₂NiF₄-type structure were measured at 4.2 K. A very large hyperfine interaction with the¹⁴¹Pr nucleus was observed. The results were analyzed based on the weak field approximation, andgvalues and hyperfine coupling constantsAwere obtained. The measuredgvalues are much smaller than ∣−10/7∣, showing that the crystal field effect on the behavior of a 4felectron is large. The value of ∣g∣ decreases from 0.646 (Pr⁴⁺/Ba₂SnO₄) to 0.615 (Pr⁴⁺/Sr₂SnO₄), which is caused by the increase of the crystal field due to the shrinking of the lattice. In contrast, the hyperfine coupling constants are almost constant:A=0.0605 cm⁻¹.     

Covalent Bonding and Hyperfine Interactions in Mo(V) Oxo Halide Complexes

Optical and EPR data were used to analyze delocalized bond structures in the antibonding and bonding states of complexes MoOL₅ (L = Cl and Br). Covalent bond parameters were calculated with consideration of charge-transfer states (CTS). The effects of CTS on the components of the g, A, and A ^L tensors were estimated; the third-order corrections for the EPR parameters were calculated. The role of CTSs for interpretation of the parameters of the additional hyperfine interaction was noted.     

An e.p.r. study of tetradentate Schiff base copper complexes with an N–(CH2)n–N,n = 3–6 backbone

Cu^II complexes of Schiff-base ligands with a general formulation o-HOC₆H₄CH=N–(CH₂) _n –N=CHC₆H₄OH-o, where n = 3–6 have been prepared and their e.p.r. spectra investigated in order to determine the effect of the flexible methylene backbone length on the structure. The room temperature and 77 K e.p.r. spectra of the compounds, n = 3 and 4, are typical of the axially symmetric ground state with g > g . When n = 5, on the other hand, the complex gives an isotropic spectrum at room temperature. For n = 6, g appears to be greater than g . The g _iso value increases gradually from n = 3 to n = 6 indicating deviation from planarity. Simulation of the 77 K spectrum for n = 6 shows the presence of two distinct Cu²⁺ sites of equal probability. The Q-band spectrum of this compound exhibits a narrowed g signal indicative of exchange coupling. The spectrum is a consequence of intermolecular electron exchange giving a pseudo d² _z state.     

Synthesis,structure and spectroscopic properties of CuL(MeOH), H2L = (E)-N 1-(2-((2-aminocyclohexydiimino)(phenyl)methyl)-4-chlorophenyl)-N 2-(2-benzyl-4-chlorophenyl)oxalamide

A new kind of copper(II) complex, CuL(MeOH) (H₂L?=?(E)-N ¹-(2-((2-aminocyclohexydiimino)(phenyl)methyl)-4-chlorophenyl)-N ²-(2-benzyl-4-chlorophenyl)oxalamide) has been synthesized and its structure determined by single-crystal X-ray methods. Copper(II) ion is five-coordinate, bonding to four nitrogen atoms from H₂L and one oxygen atom from MeOH. Hydrogen bonds in the crystal result in the formation of a one-dimensional structure. EPR spectra are discussed. Computer simulation gave g_||?=?2.200, g_⊥?=?2.002. On the basis of the synthesis and the crystal structure, the mechanism of the metal template reaction involved in the formation of the complex was verified.