Spin transitions in non-classical systems

Peculiarities of synthesis of chain polymeric, copper(II) hexafluoroacetylacetonate based complexes with stable nitroxyl radicals and the results of studies on correlations between the magnetic properties and structure of these compounds are summarized. Temperature variation causes structural rearrangements in the solid phases of the compounds, accompanied by the magnetic effects similar to spin crossover phenomena. Magnetic anomalies induced by phase transitions originate from specific motions in the Jahn—Teller coordination units containing two types of exchange clusters, Cu²⁺—O^·—N< or >N—^·O—Cu²⁺—O^·—N<, and are accompanied by significant changes in the crystal volume after multiple cooling/heating cycles. Chemical methods of controlling the character and temperature of spin transitions by both the formation of solid solutions of mixed metal hexafluoroacetylacetonates with the same nitroxyl radical, {Cu_1–xM_x(hfac)₂L} (M = Mn, Ni, Co), and by the formation of solid solutions based on copper(II) hexafluoroacetylacetonate with different nitroxyl radicals, {Cu(hfac)₂L_xL_1–x}, are discussed. Specific influence of isotope substitution CH₃ CD₃ in the paramagnetic ligand on both the structure of the heterospin polymer chain and the temperature of the magnetic anomaly is discussed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2304–2325, November, 2004.     

Mutual Effect of Functional Groups and the Radical Center on the Reactivity of Nitroxyl Radicals

This review considers the correlation between the reactivity of nitroxyl radicals (piperidine, pyrroline, pyrrolidine, imidazoline, dihydroquinoline, tetrahydroquinoline, diphenyl nitroxide, etc.) and their chemical structure in terms of the rate constants of reactions between these radicals and hydrazobenzene. 4,4′-Di(tert-butyl)diphenyl nitroxyl has the highest reactivity, and the nitroxyl radical of benzoindolopyrrolidine is the least reactive (the difference is a factor of ∼10⁴). The effects of the metal atom in stable organometallic nitroxyl radicals and of the halogen atom in halogenated nitroxyl radicals on the reactivity of the nitroxyl center are considered. Data on the effect of the nitroxyl center on the reactivity of functional groups in the piperidine nitroxyl radical are generalized. Nitroxyl radicals with an activated double bond are shown by quantum chemical calculations to form cyclic transition complexes with amines, involving both the paramagnetic center and a double bond. This explains why the activated double bond in nitroxyl radicals is more reactive in nucleophilic additions of amines than the same bond in their diamagnetic analogues. The rate constants of nitroxyl reduction with hydrazobenzene and of nitroxyl oxidation with tetranitromethane are related to the σ_ESR constant derived from isotropic hyperfine coupling constants HFC_(aN), and their correlation with Hammett constants is demonstrated. The role of solvents in the reduction and oxidation of the nitroxyl radicals is considered. The influence of hydroxyl radical-polar solvent complexes and hydroxylamine-polar solvent H complexes on the course of reactions is considered for hydrogen atom transfer in systems of a sterically hindered nitroxyl radical and hydroxylamine.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 506–528.Original Russian Text Copyright © 2005 by Malievskii, Shapiro.     

Effect of the chemical structure of nitroxyl radicals on their reactivity in the reaction with hydrazobenzene and tetranitromethane

The reaction rate constants of reduction of stable radicals of different classes by hydrazobenzene in hexane at 20C, in the range of 0.4–5·10³ M^–1sec^–1, were determined; a single scale of the oxidative properties of stable nitroxyl radicals was constructed. The rate constants of oxidation of a series of nitroxyl radicals by tetranitromethane in aqueous medium at 20C, in the range of 0.06–10 M^–1·sec^–1, were determined. It was shown that the oxidative properties of the nitroxyl group decrease slightly with an increase in its reducing properties for nitroxyl radicals of the piperidine and imidazoline series in reactions with ascorbic acid and tetra-nitromethane in aqueous medium, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2575–2582, November, 1990.     

Oxidation of nitroxyl radicals by xenon difluoride

Conclusions Oxoammonium fluorides have been prepared for the first time by oxidizing nitroxyl radicals with xenon fluoride. Nitroso compounds are formed in the oxidation of piperidinoxyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 572–576, March, 1978.     

Progress in the chemistry of the cycloartanes

The review, which considers advances in the chemistry of the cycloartanes, covers literature devoted to compounds of plants of the genusAstragalus and other publications appearing in the period from 1984 to 1987 and, in part, 1988.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 156–175, March–April, 1989.     

Synthesis of new diacetylenic monomers containing nitroxyl radicals

A series of new symmetrical and asymmetrical disubstituted diacetylenic monomers containing piperidine and carboline nitroxyl radicals were synthesized. These compounds are starting reagents for the synthesis of polyconjugated high-spin species.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 226–230, January, 1991.     

Nitroxyl-radical rotational-mobility anisotropy effects in magnetization-transfer electron spin echo

Formulas have been derived for the magnetization transport in the limiting case of uniaxial rotation and any reorientation correlation (Ivanov-Valiev model). Numerical calculations have been performed for particular situations. Rotational-mobility anisotropy makes itself felt when the difference in the angles between the symmetry axis for the nitroxyl radical magnetic tensor and the rotation axis is less than 30° or close to 90°.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 647–653, November–December, 1989.     

A New Page in the Chemistry of Copper: Compounds Containing [CuCl6]4– and [CuBr6]4– Anions

A review of the methods used to synthesize compounds containing isolated [CuCl₆]^4– and [CuBr₆]^4– anions is given. The results of studies of new compounds using X-ray diffraction analysis, steady-state magnetic susceptibility, EPR, IR, and electronic spectroscopy are discussed.     

Synthesis,reactions, and properties of some selenides of the thiophene,furan, and selenophene series (review)

The review is devoted to the authors' research on the synthesis and study of the reactivities of selenides of the thiophene series, and, to a lesser extent, of selenides of the furan and selenophene series. The properties of the indicated compounds — their capacity for reaction with electrophilic agents and organolithium compounds — and their spectral characteristics are examined in order to compare them with the properties of the corresponding sulfides and alkoxy derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 723–737, June, 1972.     

Spintronics and spintronics materials

The review concerns the fundamentals of spintronics (spin-transport electronics). The material covers spin-spin interactions and spin relaxation in semiconductors as well as spin and spin injection related effects in the condensed matter. Examples of promising spintronic devices are given, requirements for spintronic materials are formulated, methods of synthesis of spintronic materials are described, and the physicochemical properties of some materials are characterized. Organic spintronic materials are briefly outlined and the state-of-the art in the field of research on inhomogeneous magnetic semiconducting materials possessing high-temperature ferromagnetism is described. The emphasis is placed on the chemical bonding and electronic structure of magnetic impurities in semiconductors, consideration of the nature of ferromagnetism, and on the character of exchange interactions between localized spins in novel spintronic materials.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2255–2303, November, 2004.     

Phase transfer catalysis in the chemistry of heterocyclic compounds. A review

This review covers new data on the use of phase transfer catalysis in the chemistry of heterocyclic compounds. The following reactions are considered: alkylation, acylation, reactions with dihalocarbenes, preparations of ethers and esters, the formation of halo derivatives, oxidation and reduction, and isotope exchange. The advantages of phase transfer catalysis are examined and the prospects for its further development in heterocyclic chemistry are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1443–1459, November, 1983.     

Synthesis and some reactions of sterically hindered 3-imidazoline 3-oxides

Sterically hindered 3-imidazoline 3-oxides were obtained by condensation of -amino oximes with ketones. It is shown that the reaction of these compounds with electrophilic agents takes place at both the nitrone grouping and the amino group. The oxidation of the products makes it possible to obtain stable nitroxyl radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 103–109, January, 1979.     

Reaction of nitroxyl radicals with dichlorocarbene

Conclusions The reaction of aromatic nitroxyl radicals with dichlorocarbene, generated under phase transfer catalysis conditions, leads to the corresponding hydrazine derivatives through the abstraction of the oxygen atom from the nitroxyl radicals and formation of aminyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 470–472, February, 1989.     

Nitroxyls and PELDOR: Nitroxyl radicals in pulsed electron-electron double resonance spectroscopy

The review considers the main propositions of PELDOR theory. It is shown how from the analysis of PELDOR time traces it is possible to find the parameters of a spin system such as the distance and the distance distribution (spectrum), number of spins in aggregates and complexes, exchange integral and how to separate for the following analysis the inter- and intramolecular contributions to the general dipole interaction. Examples of PELDOR application in the studies of the spatial distribution of nitroxyl radicals, the charge effect of dipolar interacting nitroxyls on their spatial distribution are given and the results of the determination of distances and the spectrum of distances for nitroxyl bi-, tri-, and tetraradicals are presented. The works on nitroxyl radicals in which the orientation selectivity effect, spin exchange, and conformational properties of the radicals are examined by the PELDOR method are analyzed. The studies of the structure of paramagnetic ion-nitroxyl radical pairs and the PELDOR data on nitroxyls at high frequencies (high fields) are considered. The last section of the review is devoted to the works examining the properties such as the molecular flexibility of oligomers and supramolecules contains nitroxyl radicals.     

Magnetic properties of tetrameric μ3-methoxophenolates of nickel(II)

The magnetic properties of the tetranuclear nickel(II) complexes[Ni(OCH₃)(L) (CH₃OH)]₄ (L stands for a residue of 2,4,6-trichlorophenol or 2,4-dinitrophenol) have been investigated. The variation of the effective magnetic moment (per metal ion) with the temperature for both compounds points out the presence of a ferromagnetic exchange interaction. When the magnetic properties of these compounds are described, agreement with the experiment is achieved, if it is taken into account that there is a weak ferromagnetic intercluster interaction in addition to the Isotropic intracluster Heisenberg interaction. It has been established on the basis of a comparison of the data obtained and the literature data that changes in the Ni-O-Ni angle in the 90±14° range have little influence on the value of the parameter J, while a decrease in the Ni-O_br. distance causes an increase in J.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, 285–291, May–June, 1986.     

Heterocyclic enamides — Derivatives of imidazolidine nitrosyl radicals: Reactions with nucleophilic and electrophilic reagents

The reactions of the heterocyclic enamides — 4-alkyliden-2,2,5,5-tetraalkyl-3-formylimidazolidin-1-oxyls — with organomagnesium and organolithium compounds takes place at two reaction centers — the N-formyl group and the C=C endocyclic carbon atom — to give three types of product: 3-imidazoline derivatives, substituted formyl derivatives, or acyclic nitroxyl radicals. Enamides with POCl₃ in DMF gives products of electrophilic substitution at the exocyclic methylene group with retention of the N-formyl.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 620–624, May, 1988.     

Stable nitroxyl radicals with a hydrogen atom at α-carbon atom of nitroxyl group

Nitroxyl radicals containing the diphenylmethyl group as one of the substituents at the nitroxyl group are stable compounds that can be isolated in an individual state.N-(2-Hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 400–408, February, 1996.     

Reaction of dihydropyrazine-1,4-dioxides with organolithium compounds. Synthesis of nitroxyl radicals — derivatives of tetrahydropyrazine oxide

Reaction of dihydropyrazine-1,4-dioxides with organoiithium compounds followed by oxidation with MnO₂ gives stable nitroxides of the pyrazine series. The reaction of a pyrazine containing methylnitrone groupings with ethylbenzoate in the presence of NaH or PhLi leads to mono- or diphenacyl derivatives, which have been shown to exist in solution as a mixture of tautomers. On treatment with hydroxylamine and subsequent oxidation the monophenacyl nitrone derivative yields a stable nitroxyl radical derived from spiroisoxazolopyrazine.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 927–931, May, 1993.     

New stable nitroxyl radicals from hydrogenated quinolines

Conclusions Syntheses were reported for 6-triphenylmethyl derivatives of 2,2,4-trimethyl-1,2-dihydroquinolines and 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines as well as 4-phenpl-1,2,3,4-tetrahydroquinoline. The oxidation of these compounds by H₂O₂ in the presence of Na₂WO₄ and also by m-chloroperbenzoic acid gave nitroxyl radicals, whose structures were supported by EPR spectroscopy.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimichesksya, No. 12, pp. 2870–2873, December, 1988.     

Characteristic and spectroscopic properties of the Schiff-base model compounds

Two series of conjugated aromatic imines (Schiff-base model compounds) with different central groups and various side-group substitutions have been synthesized and characterized by elemental analysis, differential scanning calorimetry (DSC) technique, hydrogen nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FTIR) and ultra-violet and visible light (UV–vis) spectroscopy measurements. The UV–vis absorption of solutions of these compounds in dimethylacetamid (DMA), chloroform and methanol was investigated in the optical range from 240 to 450 nm, where two distinct absorption bands: at 250–280 and 315–360 nm with the different level of absorption have been observed. The influence of compound molecular structure and polarity of solvent on the absorption spectra and the possible optical transitions have been discussed. Structure of diamines in the azomethine models fundamentally affected their spectroscopic properties and conjugation of π-electrons.