Powder ESR Spectra Research Articles

Spectroscopic and electrical properties of oxidized tris(dmit)vanadium anion complexes (dmit = 4,5-dimercapto-1,3-dithiole-2-thionate)

Several oxidized tris(dmit)vanadium anion complexes (dmit 2− = the 4,5-dimercapto-1,3-dithiole-2- thionate anion) were prepared; [FeCp 2] [V(dmit) 3] (Cp − = the cyclopentadienyl anion), [Fe(MeCp) 2][V(dmit) 3] (MeCp − = the methylcyclopentadienyl anion), [Fe(Me 5Cp) 2] [V(dmit) 3] (Me 5Cp − = the pentamethylcyclopentadienyl anion), [NiCp 2][V(dmit) 3], Fe(V(dmit) 3] 2·3H 2O, and Co(V(dmit) 3]·3H 2O. They behave as semiconductors with electrical conductivities of 1 × 10 −7 to 1 × 10 −4 S cm −1 measured for compacted pellets at 25 °C. On the basis of powder electronic reflectance, IR, ESR, and X-ray photoelectron spectra, electronic states of the complexes and interactions among the anion moieties are discussed.

A study of electron spin resonance phenomena in TeO2-CuO-CuCl2 glasses

We present the results of ESR powder spectra taken on unannealed glass samples having the composition 65TeO 2 -(35-x)CuO-xCuCl 2 with x varying from 1 to 5 in mol%. ESR studies were carried out tube at room temperature and at X-band frequency

The simulation of powder ESR spectra of organic free radicals

The simulation of powder ESR spectra of organic free radicals

Copper(II) Complexes of Acyldihydrazones

Abstract Copper(II) complexes of disalicylaldimine oxamide (H4A), malonamide (H4B), succinamide (H4C), glutaramide (H4D), adipamide (H4E), and phthalamide (H4F) have been synthesized in aqueous-alcoholic media and characterized by elemental analyses, thermoanalytical data, decomposition temperature, magnetic moments, infrared and electronic and electron spin resonance spectral studies. All the complexes were found to have the compositions Cu2(L)nH2O (where H4L = H4A, H4B, H4C, H4D, H4E, and H4F, n = 2 and 4). These complexes possess square pyramidal configuration except disalicylaldimine oxamido and phthalamido complexes which possess tetragonally distorted octahedral stereochemistry. All the complexes show sub-normal magnetic moments. The magnetic moments coupled with powder ESR spectra in the solid state at room temperature indicate strong metal-metal interaction. The infrared spectra reveal that the ligands react in the enol form as tetrabasic hexadentate ligands. On the basis of the magnitude of shift...

Crystal and molecular structure of a copper(II)-glycinehydroxamic acid complex

Crystals of trans-bis(glycinehydroxamato)copper- (II) dihydrate (CuC 4H 10N 4O 4·2H 2O) were obtained by mixing concentrated solutions of copper(II) perchlorate and glycinehydroxamic acid (H 2NCH 2- CONHOH) in a 1:2 molar ratio and adjusting the pH to about 8. X-ray crystallographic data show the crystals to be orthorhombic: Pbca, a = 5.052(3), b = 11.152(2), c = 17.876(2) Å, V = 1007 Å 3, Z = 4. The copper ion lies on an inversion center, in which it is octahedrally coordinated by four nitrogens and two oxygens from neighboring molecules. IR spectra of the complex confirm these crystallographic results. The ESR powder and dilute solution spectra are characteristic of axial symmetry with respectively g‖ = 2.198, g⊥= 2.083 and g‖ = 2.196, g⊥= 2.055 and A Cu‖ = 202 gauss, A Cu⊥= 30.2 gauss and A N‖ = 15 gauss.

ChemInform Abstract: ESR Study of CH3CNSSN′, C6H5CNSSN′, and SNSSN′ + Free Radicals.

AbstractIsotropic and powder ESR spectra are recorded for the title radicals (I)‐(III), prepared from the dimers.

ESR Studies on Salicylaldehyde Schiff Base Complexes of Copper(II). I. Bis(N-cyclohexyl- and N-cycloheptyl-salicylideneaminato)copper(II) Complexes and Their Derivatives in Polycrystals

Abstract Twelve of the title complexes including color isomers show powder ESR spectra of various line shapes. These complexes are a novel series of copper(II) complexes which have very weak intermolecular spin-exchange interactions in crystals. Brown complexes and most green complexes show monomer and dimer ESR spectra, respectively. It is demonstrated by ESR measurements that the above green complexes are transformed into the brown ones only by grinding those green crystals finely and forcefully with agate mortar and pestle.

Generalized theoretical treatment of axially symmetric ESR hyperfine centers under slow orientational diffusion motion

The ensemble averaging based on the solution of an isotropic diffusion equation is employed to calculate analytical expressions for angular-dependent motional linewidths and shifts in spectral line position of axially symmetric ESR hyperfine centers, which undergo isotropic, small-angle, slow-orientational diffusion motion. The resultant theoretical expressions are consistent with those calculated by other investigators using different theoretical approaches. As a result of the present calculations, the entire ESR hyperfine spectra associated with slow-tumbling motions can be calculated in polycrystalline/amorphous substances. A detailed investigation of these theoretical spectra supports the validity of the previously proposed simple method of determining experimental rotational correlation times from the behavior of the parallel-edge lines of nitroxide ESR powder spectra.

Powder ESR spectra of paramagnetic impurities in axial symmetry sites

The resonance fields and amplitudes of the powder ESR spectra of paramagnetic impurities in axial symmetry sites have been computed as functions of the zero-field splitting parameter D for an effective spin S in the range 1⩽S⩽ 5 2 . The results, which are presented in graphical form, may be used for the interpretation of powder spectra.

New method of characterizing slow-tumbling motions for nitroxide spin labels/probes from second-derivative ESR powder spectra

A simple, direct method is proposed for characterizing the extent of slow-tumbling molecular motions of nitroxide spin labels or spin probes in amorphous substances. This method essentially consists of determining accurate values for the ’’single-crystal,’’ first-derivative peak-to-peak linewidths of nitroxides from their second-derivative hyperfine power spectra and hence employing the dependence of the linewidths on the nitrogen nuclear-spin-magnetic quantum number M resulting from molecular motion.

ChemInform Abstract: COMPLEX FORMATION OF ADENINE AND 9‐METHYLADENINE WITH TRANSITION METAL SALTS IN ETHANOL

AbstractDurch Rückflußkochen ethanolischer Lösungen der Metallsalze mit den Liganden im molaren Verhältnis von Metall zu Adenin von l :2 bzw. Metall zu Methyladenin von 1:1 wurden die Komplexe (I) bis (V) dargestellt.

X-band ESR powder spectrum and related magneto-microwave effects of CuF 2.2H 2O

A computer simulation of the ESR powder spectrum of CuF 2.2H 2O is carried out, and an automatic fitting procedure permits us to obtain the principal g values and crystallite linewidth. For this compound, microwave Faraday and Cotton- Mouton-Voigt effects related to ESR have been measured at X-band and room temperature. Then, the computer simulations is applied to the magneto-microwave effects by substituting for the ESR lineshape function the various crystallite lineshape functions corresponding to the rotation and ellipticity of elementary Faraday and Cotton-Mouton-Voigt effects. The computer simulations of the magneto-microwave powder effects are in close agreement with experimental data.

Calculation of powder ESR spectra of radicals with hyperfine and quadrupolar interactions. Application to mono- and dichloroalkyl radicals

A FORTRAN program has been written which calculates powder ESR spectra for a paramagnetic system with S = 1 2 described by the spin-Hamiltonian H = β1 Bg S + Σ i=1 n { S i A i I i + I i Q i I i − β N g i BI i }; under the assumption that the electronic Zeeman term is the dominant interaction. The perturbation matrix consisting of the hyperfine, quadrupolar. and nuclear Zeeman terms of each nucleus is diagonalized. The g, A, and Q tensors need not have parallel principal axes. A Gaussian or a Lorentzian linewidth is superimposed on the calculated stick diagram and integration over all orientations is performed by Gaussian quadrature. Powder spectra of mono- and dichloroalkyl radicals have been generated using this program.

Complex formation of adenine and 9‐methyladenine with transition metal salts in ethanol

AbstractThe coordination chemistry of adenine and 9‐methyladenine towards transition‐metal ions has been studied. Solid compounds of the formula M(AH)2X2 were isolated and characterised for M = Ni, Cu, Zn and Cd and X = Cl, Br, NO3 and ClO4; AH standing for adenine. With 9‐methyladenine (MA) solid compounds formulated as M(MA)X2(M = Co, Ni, Cu, Zn and Cd; X = Cl and Br) and formula M(MA)2(NO3)2‐nH2O (M = Co and Ni with n = 2 and M = Cu, with n = 1) have been synthesized.The compounds were characterised by chemical analysis, infrared spectra, far‐infrared spectra, ligand‐field spectra, X‐ray powder diagrams, ESR powder spectra and magnetic susceptibility measurements. Despite several attempts, no compounds containing more than two of these ligands per metal ion could be òbtained. Extensive ligand‐ligand and ligand‐anion hydrogen bonding may account for this result.With a few exceptions adenine appears to coordinate via N(9) in monomeric compounds and via N(3) and N(9) in dinuclear compounds. The respective coordination sites in 9‐methyladenine complexes are N(7) in the case of monodentate coordination, and N(1) and N(7) in the case of bidentate bridging coordination.

Intermediates of radiation-induced polymerisation of maleimides studied by ESR

Radicals produced by radiolysis and photolysis of maleimides (maleimide, N-methylmaleimide, N-ethylmaleimide, N-phenyl-maleimide) in bulk have been identified by ESR spectroscopy. γ-Irradiation of maleimides yields up to five different radicals depending on the type of maleimide. Because of the great linewidth of powder ESR spectra, the hyperfine splittings are determined by means of computer simulation. For N-alkyl maleimides the starting species of polymerisation are formed by abstraction of a H-atom from the alkyl group in radiolysis as well as in photolysis. The structure of the propagating radical shows that polymerisation proceeds via the ethylenic double bond. The detection of maleimide ions makes participation of these ions in polymerisation conceivable. Radiolysis of maleimide and N-phenylmaleimide yields the same type of radicals whereas only ions could be detected after u.v.-irradiation.

X-band ESR faraday and cotton-mouton-voigt effects of CuCl 2 · 2H 20 and Cu(NH 4SO 4) 2 · 6H20 in polycrystalline powder

Magneto-microwave Faraday and Cotton-Mouton-Voigt effects related to anisotropic ESR powder spectra were studied at X-band and room temperature on polycrystalline samples of CuCl 2·2H 2O and Cu(NH 4SO 4) 2·6H 2O. For both compounds, computer simulations of the powder ESR spectra were carried out with a rather simplified model accounting for a crystallite Lorentzian lineshape and complete anisotropies of the g factor, transition probability, and linewidth. One observes a good agreement between simulated and experimental spectra, and an automatic fitting procedure permits one to obtain for each compound the principal values of the g factor and linewidth, in close agreement with results from previous single-crystal ESR studies. The same model is then transposed to the magnetomicrowave effects, by substituting for the ESR lineshape function the various crystallite lineshape functions corresponding to the rotation and ellipticity of elementary Faraday and Cotton-Mouton-Voigt effects. Computer simulations of the magneto-microwave powder effects are in close agreement with experimental data.

Über Galvinole und Galvinoxyle, III. EPR-Spektroskopie an regellos orientierten Bis-Galvinoxyl-Biradikalen in der Glasmatrix / On Galvinols and Galvinoxyls, III. EPR Study of Zero Field Splitting in Randomly Oriented Galvinoxyl Biradicals

ESR powder spectra of several differently bridged bis-galvinoxyl biradicals have been recorded. The spectra can be interpreted in terms of a weak electron-electron dipolar coupling between the unpaired spins of randomly oriented triplet molecules. Using MO-theory and a point charge model for atomic orbitals a detailed structural analysis is performed on the basis of quantum mechanical calculations. Taking into account the twist angles between the various aryl rings the experimental data can be explained satisfactorily.

Synthese und EPR-spektroskopie dicyclopentadienylanaloger der schlenkschen und tschitschibabinschen kohlenwasserstoffe

The synthesis of several hydrocarbon biradicals consisting of two tetraphenylcyclopentadienyl moieties with different bridge fragments is described. The ESR powder spectra show that there is an intramolecular coupling of two unpaired electron spins to a triplet spin state. The magnitude of the zero field splitting (zfs) is used to discriminate between different molecular conformations. More detailed structural informations are obtained from the observed zfs by quantummechanical calculations of the zfs-parameter D as a function of various torsional angles and cis- or trans-orientations of molecular fragments. The behaviour of the four highest occupied MO's with respect to structural changes in the biradicals is discussed.

Strukturuntersuchung an biradikalen vom typ des schlenk'schen und des tschitschibabin'schen kohlenwasserstoffs

The synthesis of various hydrocarbons of the Schlenk and Tschitschibabin type with differently bridged dibiphenylylmethyl moieties is presented. The ESR powder spectra of these two-spin systems show line shapes typical for intramolecular triplet states. The molecular conformation is studied qualitatively on the basis of the magnitude of the zero field splitting parameters and simple molecular models. A more detailed structural analysis is performed on the basis of quantummechanical calculations of these parameters using MO-theory and a point charge model for atomic orbitals. These calculations take into account the twist angles between the various phenyl rings and the cis or trans positions of the points of maximum spin density in the different moieties. A possible classification of the various two-spin systems according to their magnetic properties is discussed.

Linewidth variations of ESR spectra in solid state

A statistical model is proposed to explain the linewidth variation of the hyperfine multiplet in the solid state (powder or glass) ESR spectra for Mn(II)- and VO(II)-polygalacturonate as well as Co(II)-dimethylglyoxime. Considering the local magnetic field and the principal values of tensors in the spin Hamiltonian as random variables, we obtain the following linewidth variation formula: W M=(α+βM+γm 2) 1 2 . The linewidth variation determined by the accurate simulation of ESR spectra is in good agreement with the proposed formula. In all our examples the major contribution to the linewidth is inhomogeneous distribution of the ligand field.