Computer calculations on ESR spectra

Conclusions These computations on ESR spectra provide useful general suggestions for approximate analyses of unresolved ESR spectra; means of more rigorous analysis are also indicated. It is probable that the theoretical spectra and nomograms will provide a means of facilitating the various methods of analysis as applied to ESR spectra; this should make ESR methods all the more valuable for a variety of purposes.Translated from Zhurnal Strukturnoi Khimii, Vol. 2, No. 6. pp. 690–695, November–December, 1961     

Quick method for analysis of anisotropic ESR spectra of particles with a g factor having rhombic symmetry in partially ordered and unordered systems

The exact integral expression describing the form of the anisotropic ESR spectrum of particles with a g factor having rhombic symmetry and a spin S=1/2 has been expanded into a rapidly converging series. This has made it possible to formulate simple rules for the quick analysis of experimental spectra in the case of individual absorption lines with Gaussian and Lorentzian shapes and to determine the corrections associated with the approximate nature of the approach. The rules obtained are universal, i.e., they are equally valid for the ESR spectra of both unordered and partially ordered systems. They can be used to determine the components of the g factor, the width of an individual absorption line, and the orientational distribution functions of the particles in a sample from spectra with sufficient accuracy. The applicability of the expressions obtained has been demonstrated by comparing them with exact computer-simulated ESR spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 738–742, November–December, 1988.     

Reactions of potassium dibenzo-18-crown-6 pentacyanocobaltate(II) with some lewis bases

ESR has been applied to the interactions of [K(DBC)]₃[Co(CN)₅], in which DBC is dibenzo-18-crown-6, in methanol solution with triphenylphosphine, pyridine, and triethylamine. The ESR spectra are described for the paramagnetic [(NC)₅CoB]^3– adducts, where B is triphenylphosphine or pyridine.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 25, No. 2, pp. 234–237, March–April, 1989.     

Cation-radicals in the electrochemical oxidation of 1,2,6-trimethyl-3,5-diacetyl-1,2-dihydropyridines

The ESR spectra of the cation-radicals of 4-substituted 3,5-diacetyl-1,2,6-trimethyl-1,2-dihydropyridines were generated electrochemically by oxidation in acetonitrile at –40°C. The unpaired electron distribution in the cation-radicals was established by analysis of the hyperfine structure of the ESR spectra. It was found that the size of the electrochemical oxidation potential of the compounds and the unpaired electron distribution in the cation-radical were subject to the inductive effect of the substituents in positions 3 and 5 of the heterocycle.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 772–775, June, 1997.     

ESR spectra of copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones

ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H₄L) [Cu₂L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant 40·10^–4 cm^–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant 72·10^–4 cm^–1, which is common for the copper(ii) monomeric compounds.     

Spectral study of reactions of La@C82 and Y@C82 with amino-containing solvents

A solvent effect on the electronic absorption UV-VIS and ESR spectra of La@C₈₂ and Y@C₈₂ was found. The UV-VIS spectra of La@C₈₂ in pyridine, dimethylformamide, and hexamethylphosphorotriamide are identical with that of the La@C₈₂ ^– anion, which is evidence for La@C₈₂ reduction in these solvents. In amino-containing solvents, the shape of the ESR spectra depends on the temperature and the time of preparation of the solutions. Changes in the ESR spectra of La@C₈₂ and Y@C₈₂ in dimethylformamide are due to functionalization of these compounds upon reduction.     

Determination of the orientation distribution function of anisotropic paramagnetic species from the angular dependence of the ESR spectra

A method for determination of the orientation distribution function of anisotropic paramagnetic species from the angular dependence of the ESR spectra based on simulation of the spectra was developed. The orientation distribution function is represented as a sum of orthonormal functions. The weight coefficients are determined by minimizing the deviations of the theoretical spectra from experimental ones. The method was numerically tested. The method is relatively insensitive to the presence of noise and foreign ESR signals not related to the sample orientation in the magnetic field.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2595–2601, December, 2004.     

Sterically crowded chelate complexes of copper(II) with phenoxazinyl ligands: ESR study

A copper complex with 1-H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazinyl free radical ligands was synthesized, and its magnetic properties and ESR spectra were measured at 77–290 K. It was shown that a ground electron state with one unpaired electron is typical of this complex at 77–290 K. The magnetoresonance parameters of this complex are characterized by ag-factor value (1.978) that is rather unusual for copper-containing compounds and by hyperfine coupling due to Cu nuclei. The considerable broadening of ESR spectral lines with increasing temperature is probably not due to the formation of a quartet state (S=3/2). A model of electron states of the compound investigated was developed in the framework of ligand field theory, which made it possible to explain the pattern of the ESR spectra, which were untypical of copper complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 894–899, May, 1995.This study was financially supported by the International Science Foundation (Grant NRT 000).     

Influence of the conjugate anion on the parameters of ESR spectra in radical cations of sterically hindered hydroquinones

The reactions of hindered p-quinones and hydroquinones with inorganic, organic, and Lewis acids have been studied by ESR. The conjugate anion has a strong perturbing effect on the distribution of the spin density at the reaction center. A mechanism for the reduction of p-quinones and the oxidation of hydroquinones, which includes a step involving the formation of radical-cation salts, has been proposed. The form of the ESR spectra and the composition of the final products are greatly dependent on the ratio between the reactants, the medium, and the temperature.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 737–741, November–December, 1986.     

Destruction of silicon-containing phenoxy radicals

Conclusions It was shown that the destruction of silicon-containing phenoxy radicals in benzene is second order by means of ESR and spectrophotometric methods.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 572–574, March, 1972.We thank G. A. Abakumov for obtaining the ESR spectra and I. A. Chuev for his assistance in carrying out the spectrophotometric studies.     

Reduction of C60 and C70 by primary amines: Optical and ESR studies

Radical anions C70- and C70 2- were obtained in vacuo by the reaction of I-amino3-propanol (AP) and 1,5-diaminopentane (DAP) with fullerene C70. The radical anions were identified by visible/near IR (X = I372 and I172 nm, respectively) and ESR spectroscopies. The temperature dependences of the ESR spectra were studied for the C₆₀-AP, C₇₀-AP, and C70-DAP systems. At low temperatures (I5-45 K), the ESR spectrum for C60 is close to that for species with axial symmetry of theg-factor (q_| = 2.000 and g, = I.995). The anisotropy of theg-factor is averaged, when the temperature increases. At T > I48 K the averaged line is broadened, and the sharp signal with g = 2.0001 overlaps this broad line. The intensity of the narrow line increases, when the temperature increases. The ESR spectrum observed in the C₇₀-AP system at I2.5 K may be tentatively described as a superposition of two ESR spectra, namely, the ESR spectra of a radical with g_| = 2.0042 and g, = 2.0015 (presumably a radical cation) and of C₇₀ ^– with q_| = 2.000 and g = I.994. The spectra of the sample in which C70 is present mainly as C₇₀ ^2– exhibit only a line with g = 2.0004.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 103–108, January, 1996.     

ESR spectra of sterically hindered silicon-containing phenoxyls

The ESR method was used to study a series of sterically hindered silicon-containing phenoxyls — 2-trialkyl(dialkylalkoxy)silyl-4,6-di-tert-butylphenoxyls. The parameters of the ESR spectra were determined: the constants of splitting of the unpaired electron on meta-protons of the phenoxyl ring, protons of the organosilyl substituents, and magnetic silicon nuclei, as well as the spectroscopic splitting factors. The stability of the silicon-containing phenoxyls relative to one another was determined. The influence of a second Si-containing substituent in the ortho-position and an alkyl substituent in the para-position was followed on the example of 2,6-triphenylsilyl-4-tert-butylphenoxyl and the 2,6-trimethylsilyl-4-ethylphenoxyl radical. The stability of the aroxyls is determined primarily by the steric shielding of the radical site responsible for the dimerization-rearrangement reaction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 67–72, January–February, 1992.     

ESR spectrum of the oxidized vanadylporphyrin complex of Karazhanbass petroleum

As a result of the use of various oxidants, mono- and bications of the natural vanadylporphyrins of Karazhanbass petroleum have been obtained, and their ESR spectra have been studied.Institute of the Chemistry of Petroleum and Natural Salts of the Kazakh SSR Academy of Sciences, Gur'ev. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 190–193, March–April, 1990.     

Electronic and ESR spectroscopic study of thiocyanate-containing coordination compounds of titanium(III) in alcohol solutions

In an investigation of electronic and ESR spectra, it has been established that titanium(III) with the thiocyanate ion (in ethanol) forms distorted tetrahedral and octahedral complexes. The tetrahedral compounds, which are hydroxo complexes of titanium(III) that contain one hydroxyl group and three thiocyanate ions in the coordination sphere, give signals in the ESR spectra with g_o=1.960, A_o=15.0·10^–4 cm^–1 g=1.958, A ^Ti =26.4·10^–4cm^–1, g= 1.691, A^Ti=9.0·10^–4 cm^–1. In the ESR spectra of liquid solutions, additional splitting on the nitrogen atoms is manifested(A _o ^N =2.2·10^–4 cm^–1), which indicates bonding of thiocyanate ions through the nitrogen atom. The pseudo-octahedral complexes of titanium(III), containing from two to six thiocyanate ions in the coordination sphere, are characterized by d-d absorption bands in the 520–590 nm region; and at 77°K, they give anisotropic ESR signals. On the basis of the temperature dependences of the equilibrium constants for the reaction of conversion of the tetrahedral complexes to the octahedral complexes, and also the lifetimes of the tetrahedral complexes, values have been estimated for the heat of reaction (H=26.8 kJ/mole) and the entropy change (S=–1.66 kJ/mole·°K) of the equilibrium process, and also the activation energy for the reaction of titanium(III) thiocyanate formation (E=37 kJ/mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 560–567, September–October, 1985.     

Accounting for effects of AZA-substitution on hyperfine interaction constants in ESR spectra

A previously developed scheme for describing the effects of substituents on the physicochemical characteristics of molecules with conjugated bonds has been extended to systems with an open electron shell. The distribution of spin density has been found for a number of anion radicals of azines on the basis of a calculation of their hydrocarbon analogs. The results are in agreement with experimental values of the HFI constant in the ESR spectra of these compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 155–161, March–April, 1989.     

ESR spectra of free radicals of 3,3-disubstituted 1,2,3,4-tetrahydropyridines produced during electrochemical reduction

The polarographic properties (potentials, number of electrons, reversibility) of the electrochemical reduction of 3,5-diethoxycarbonyl-3-(p-nitrobenzoyl)-6-(p-nitrophenyl)-1,2,3,4-tetrahydropyridine and its derivatives in dimethylformamide have been determined. In the course of the electrochemical generation, ESR spectra of primary radical anions of p-nitrobenzoyl structure were obtained along with ESR spectra of nitrophenyl-p-substituted free radicals formed as a result of further reduction.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1103–1110, August, 1998.     

Photodynamic effects in the components of cotton seeds

The formation of a stable radical cation and of an unstable peroxide form of gossypol in the light under aerobic conditions has been established on the basis of an analysis of the ESR spectra obtained. The formation of mono- and dianions of gossypol in its alkaline solutions has been shown.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenni, No. 3, pp. 354–360, May–June, 1987.     

Nitroazines. 4. Polarographic behavior of 5-nitropyrazolo[3,4-b]pyridines and the esr spectra of their electrochemically generated free radicals

1-Methyl- and 1-phenyl-substituted derivatives of 5-nitropyrazolo[3,4-b]pyridines are reduced at a dropping mercury electrode in a single one-electron wave with the formation of radical anions in interval of potentials from –0.94 to –1.06 V. Compounds unsubstituted at the N(₁) nitrogen atom give an additional polarographic wave at E_1/2 = –1.4 V due to the reduction of the deprotonated form (anion). The potentials and HFS constants of the ESR spectra of the corresponding electrochemically generated free radicals are given.For Communication 3, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 689–693, May, 1985.     

Interaction of n-substituted phenothiazines with halogen-containing solvents

ESR spectroscopy was used to study the interaction of several N-substituted phenothiazines with halogencontaining solvents (CCl₄, CHCl₃, CH₂Br₂). The dissolution of phenothiazines in these solvents was found to be associated with an ESR signal indicating the presence of an oxidation-reduction reaction in which the halogen-containing compounds act as acceptors, and the phenothiazines act as electron donors. The HFS of the ESR spectra of the cation radicals obtained was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 274–276, February, 1996.     

Tautomerism in ion pairs of semiquinone anion radicals with ammonium cations

A study has been made of the influence of solvation factors on the kinetics and mechanism of cationotropism in ion pairs of certain semiquinone anion radicals with ammonium cations. It has been shown that the medium influences the magnetic resonance parameters of the ESR spectra of these species.Karaganda University. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 184–188, March–April, 1991. Original article submitted December 15, 1986.