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V. I. Ovcharenko - One of the best experts on this subject based on the ideXlab platform.
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Spin transition characteristics of molecular solvates of Cu^II complexes with nitroxides: sensitivity to the packing type
Russian Chemical Bulletin, 2019Co-Authors: N. A. Artiukhova, G. V. Romanenko, A. S. Bogomyakov, G. A. Letyagin, S. E. Tolstikov, V. I. OvcharenkoAbstract:A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper( ii ) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl (L^Me) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl (L^Et) of the composition [Cu(hfac)_2L^R]_2 · Solv (Solv = benzene, bromobenzene, toluene, o -xylene, p -xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular Exchange Clusters {Cu^2+-O^·-} from 2.321 to 1.974 Å. As a result, the temperature dependences of the effective magnetic moment μ_eff( T ) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μ_eff( T ) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac)_2L^R]_2 · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac)_2L^R]_2 · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin Exchange Cluster.
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Complexes of CuII with nitroxides and their magnetochemical behavior
Russian Chemical Bulletin, 2013Co-Authors: K. Yu. Maryunina, Galina V. Romanenko, E. M. Zueva, S. V. Fokin, A. S. Bogomyakov, V. I. OvcharenkoAbstract:The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)2LAll and Cu(hfac)2LBu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, LAll and LBu are 2-(1-allyl-1H-pyrazol-4-yl)- and 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert-butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μeff(T). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)2LAll, this is the phase transition accompanied by the structural rearrangement of the Exchange Cluster >N—·O—CuII—O·—N
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Complexes of Cu^II with nitroxides and their magnetochemical behavior
Russian Chemical Bulletin, 2013Co-Authors: K. Yu. Maryunina, G. V. Romanenko, E. M. Zueva, S. V. Fokin, A. S. Bogomyakov, V. I. OvcharenkoAbstract:The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)_2L^All and Cu(hfac)_2L^Bu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, L^All and L^Bu are 2-(1-allyl-1 H -pyrazol-4-yl)- and 2-(1-butyl-1 H -pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert -butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μ_eff( T ). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)_2L^All, this is the phase transition accompanied by the structural rearrangement of the Exchange Cluster >N—·O—Cu^II—O·—N
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Nonclassical Spin Transitions
Journal of Structural Chemistry, 2002Co-Authors: V. I. Ovcharenko, Galina V. Romanenko, S. V. Fokin, Vladimir N. Ikorskii, Yu. G. Shvedenkov, Evgeny V. Tretyakov, S. F. VasilevskiiAbstract:A family of heterospin polymer chain complexes Cu(hfac)2 with pyrazole-substituted nitronyl nitroxides (LR, where R = Me, Et, Pr) of the composition Cu(hfac)2LR was found. In the solid state the complexes undergo low-temperature structural rearrangements accompanied by magnetic effects analogous to spin-crossover. Polymer chains with a “head-to-head” or “head-to-tail” motif in Cu(hfac)2LR are formed as a result of the bridging coordination of LR through the imine N atom of pyrazole and one of the O atoms of the nitronyl nitroxide fragment. Despite the low-temperature structural phase transition, the single crystals retain the quality needed for an X-ray investigation, due to which the compounds may be studied at different temperatures and structural dynamics studies are possible. It was found that the major structural changes mainly occur in the coordination polyhedra, leading to phenomena analogous to spin-crossover. This rearrangement is possible due to the Jahn–Teller nature of the Cu(II) ion, which is responsible for the pulled octahedron structure of the coordination unit. The transition of the coordinated nitroxyl O atoms from the axial (dCu–O ∼ 2.2-2.4 A) to equatorial (dCu–O ∼ 2.0 A) position is accompanied by a transition of the Exchange interaction in the Cu(II)–O•–N< Exchange Clusters from weak ferromagnetic (or weak antiferromagnetic) to strong anti-ferromagnetic, compensating the spins of the Cu(II) ion and the nitroxyl fragment. The motif of the polymer chain (“head-to-head” or “head-to-tail”) proved to be inessential to the occurrence of thermally induced spin transitions. In both cases, the shortening of the Cu–O distance in the Cu(II)–O•–N< Exchange Cluster decreases the effective magnetic moment of the complex by a factor of \(\sqrt 2 \), because spin compensation occurs in only half of all coordination units (Cu(hfac)2LPr, Cu(hfac)2LMe, and Cu2(hfac)4LMeLEt). The low-temperature structural rearrangement in Cu(hfac)2LEt is unusual; it leads to longer Cu–O distances in the Cu(II)–O•–N< Exchange Cluster and to an abrupt transition from antiferromagnetic to ferromagnetic Exchange. At reduced temperatures, the unit cell volume decreased by 5-6% in all of the compounds. The cell parameters are large and so is the absolute value of the decrease (up to 400 A3). The maximal decrease in the cell dimensions was observed in the directions of the chains and in the directions of the maximal shortening of the Cu...Cu distances. Minimal compression or even extension of the cell took place in the direction of lengthening of the Cu–Ohfac distances. The single crystals of Cu(hfac)2LEt and Cu(hfac)2LPr possess high mechanical stability in repeated cooling-heating cycles.
S. V. Larionov - One of the best experts on this subject based on the ideXlab platform.
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synthesis and properties of the cu ii complexes with chiral bis e 1s 4r δ7 8 1 amino 2 para menthalidene aminohydroxy methane l a derivative of natural terpenoid r limonene crystal structure of the cu l μ cl cucl3 iso proh solvate
Russian Journal of Coordination Chemistry, 2009Co-Authors: T E Kokina, A. V. Tkachev, L. A. Sheludyakova, E. G. Boguslavskii, L A Glinskaya, R F Klevtsova, S N Bisyaev, S. V. LarionovAbstract:The Cu2LCl4 complex (I) with chiral bis{(E)-[(1S,4R)-Δ7,8-1-amino-2-para-menthalidene]aminohydroxy} methane (L — a derivative of natural monoterpenoid (R)-(+)-limonene) is synthesized. The crystal structure of the solvate of complex I[Cu(L)(μ-Cl)CuCl3] · iso-PrOH (II) is determined by X-ray diffraction analysis. Structure II is based on molecules of the [Cu(L)(μ-Cl)CuCl3] binuclear complexes in which L is the tetradentate cycleforming ligand. One Cl atom manifests the bridging function. The CuN4 Cl coordination unit is a square pyramid, and CuCl4 is a distorted tetrahedron. The iso-PrOH molecules are localized in cavities between the layers of structure II. The μeff value for complex I is 2.56 μB and indicates the absence of an appreciable interaction between the Cu2+ ions in the Cu(II)-Cl-Cu(II) Exchange Cluster. The compound CuLCl2· H2O (III) is synthesized. The μeff value for compound III is 1.6 μB. Complexes I and III are studied by EPR and IR spectroscopy.
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Synthesis and properties of the Cu(II) complexes with chiral bis{(E)-[(1S,4R)-Δ^7,8-1-amino-2-para-menthalidene]aminohydroxy}methane (L — a derivative of natural terpenoid (R)-(+)-limonene). Crystal structure of the [Cu(L)(μ-Cl)CuCl_3] · iso-PrOH sol
Russian Journal of Coordination Chemistry, 2009Co-Authors: T E Kokina, A. V. Tkachev, L. A. Sheludyakova, E. G. Boguslavskii, L A Glinskaya, R F Klevtsova, S N Bisyaev, S. V. LarionovAbstract:The Cu_2LCl_4 complex ( I ) with chiral bis{( E )-[(1 S ,4 R )-Δ^7,8-1-amino-2- para -menthalidene]aminohydroxy} methane (L — a derivative of natural monoterpenoid ( R )-(+)-limonene) is synthesized. The crystal structure of the solvate of complex I [Cu(L)(μ-Cl)CuCl_3] · iso -PrOH ( II ) is determined by X-ray diffraction analysis. Structure II is based on molecules of the [Cu(L)(μ-Cl)CuCl_3] binuclear complexes in which L is the tetradentate cycleforming ligand. One Cl atom manifests the bridging function. The CuN_4 Cl coordination unit is a square pyramid, and CuCl_4 is a distorted tetrahedron. The iso -PrOH molecules are localized in cavities between the layers of structure II . The μ_eff value for complex I is 2.56 μB and indicates the absence of an appreciable interaction between the Cu^2+ ions in the Cu(II)-Cl-Cu(II) Exchange Cluster. The compound CuLCl_2· H_2O ( III ) is synthesized. The μ_eff value for compound III is 1.6 μB. Complexes I and III are studied by EPR and IR spectroscopy.
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Synthesis, Crystal and Molecular Structures, and Properties of Optically Active Copper(II) Complexes with 3-N,N-Dimethylaminocaran-4-one-oxime
Russian Journal of Coordination Chemistry, 2001Co-Authors: S. V. Larionov, L. I. Myachina, G. V. Romanenko, A. V. Tkachev, L. A. Sheludyakova, V. N. Ikorskii, E. G. BoguslavskiiAbstract:Copper(II) complexes with 3- N , N -dimethylaminocaran-4-one-oxime (HL) were synthesized and characterized by X-ray diffraction analysis, photoelectronic, IR, and EPR spectroscopy, magnetic susceptibility, and thermal analysis methods, and their optical activities were studied. The [Cu_2(HL)_2Cl_4] complex is a dimer with weak Exchange interactions between unpaired electrons of the Cu(II) ions. The [Cu_3L_3(OH)Cl]Cl · 8H_2O structure is composed of triangular trinuclear complex cations, outer-sphere Cl^–anions, and water molecules. The Exchange parameter J for the trinuclear Exchange Cluster is –190 cm^–1. The title complexes are optically active in the visible range of the spectrum.
Elmar Bittner - One of the best experts on this subject based on the ideXlab platform.
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Replica-Exchange Cluster Algorithm
arXiv: Statistical Mechanics, 2011Co-Authors: Wolfhard Janke, Elmar BittnerAbstract:In finite-size scaling analyses of Monte Carlo simulations of second-order phase transitions one often needs an extended temperature/energy range around the critical point. By combining the replica-Exchange algorithm with Cluster updates and an adaptive routine to find the range of interest, we introduce a new flexible and powerful method for systematic investigations of critical phenomena. As a result, we gain two further orders of magnitude in the performance for 2D and 3D Ising models in comparison with the recently proposed Wang-Landau recursion for Cluster algorithms based on the multibondic algorithm, which is already a great improvement over the standard multicanonical variant.
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Replica-Exchange Cluster algorithm
Proceedings of The XXVII International Symposium on Lattice Field Theory — PoS(LAT2009), 2010Co-Authors: Wolfhard Janke, Elmar BittnerAbstract:Institut fur Theoretische Physik, Universitat Leipzig,Postfach 100920, D-04009 Leipzig, GermanyE-mail:wolfhard.janke@itp.uni-leipzig.deIn finite-size scaling analyses of Monte Carlo simulations of second-order phase transitions oneoften needs an extended temperature/energy range around the critical point. By combining thereplica-Exchange algorithm with Cluster updates and an adaptive routine to find the range of in-terest, we introduce a new flexible and powerful method for sy stematic investigations of criticalphenomena. As a result, we gain two further orders of magnitude in the performance for 2D and3D Ising models in comparison with the recently proposed Wang-Landau recursion for Clusteralgorithms based on the multibondic algorithm, which is already a great improvement over thestandard multicanonical variant.The XXVII International Symposium on Lattice Field Theory -LAT2009July 26-31 2009Peking University, Beijing, China
Uwe Krey - One of the best experts on this subject based on the ideXlab platform.
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Analyticity of the coherent Exchange Cluster approach for ferromagnetic Heisenberg spin alloys
Solid State Communications, 2002Co-Authors: Uwe KreyAbstract:Abstract It is provided that the Coherent Exchange Cluster Approach for ferromagnetic disordered Heisenberg spin systems fulfills the analyticity requirements, preserving at the same time translational invariance of the self-energy and the correct behaviour at k = 0. Analyticity is lost, if in addition to the Exchange integrals, also the single ion anisotropies are subject to randomness.
Galina V. Romanenko - One of the best experts on this subject based on the ideXlab platform.
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Complexes of CuII with nitroxides and their magnetochemical behavior
Russian Chemical Bulletin, 2013Co-Authors: K. Yu. Maryunina, Galina V. Romanenko, E. M. Zueva, S. V. Fokin, A. S. Bogomyakov, V. I. OvcharenkoAbstract:The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)2LAll and Cu(hfac)2LBu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, LAll and LBu are 2-(1-allyl-1H-pyrazol-4-yl)- and 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert-butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μeff(T). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)2LAll, this is the phase transition accompanied by the structural rearrangement of the Exchange Cluster >N—·O—CuII—O·—N
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Nonclassical Spin Transitions
Journal of Structural Chemistry, 2002Co-Authors: V. I. Ovcharenko, Galina V. Romanenko, S. V. Fokin, Vladimir N. Ikorskii, Yu. G. Shvedenkov, Evgeny V. Tretyakov, S. F. VasilevskiiAbstract:A family of heterospin polymer chain complexes Cu(hfac)2 with pyrazole-substituted nitronyl nitroxides (LR, where R = Me, Et, Pr) of the composition Cu(hfac)2LR was found. In the solid state the complexes undergo low-temperature structural rearrangements accompanied by magnetic effects analogous to spin-crossover. Polymer chains with a “head-to-head” or “head-to-tail” motif in Cu(hfac)2LR are formed as a result of the bridging coordination of LR through the imine N atom of pyrazole and one of the O atoms of the nitronyl nitroxide fragment. Despite the low-temperature structural phase transition, the single crystals retain the quality needed for an X-ray investigation, due to which the compounds may be studied at different temperatures and structural dynamics studies are possible. It was found that the major structural changes mainly occur in the coordination polyhedra, leading to phenomena analogous to spin-crossover. This rearrangement is possible due to the Jahn–Teller nature of the Cu(II) ion, which is responsible for the pulled octahedron structure of the coordination unit. The transition of the coordinated nitroxyl O atoms from the axial (dCu–O ∼ 2.2-2.4 A) to equatorial (dCu–O ∼ 2.0 A) position is accompanied by a transition of the Exchange interaction in the Cu(II)–O•–N< Exchange Clusters from weak ferromagnetic (or weak antiferromagnetic) to strong anti-ferromagnetic, compensating the spins of the Cu(II) ion and the nitroxyl fragment. The motif of the polymer chain (“head-to-head” or “head-to-tail”) proved to be inessential to the occurrence of thermally induced spin transitions. In both cases, the shortening of the Cu–O distance in the Cu(II)–O•–N< Exchange Cluster decreases the effective magnetic moment of the complex by a factor of \(\sqrt 2 \), because spin compensation occurs in only half of all coordination units (Cu(hfac)2LPr, Cu(hfac)2LMe, and Cu2(hfac)4LMeLEt). The low-temperature structural rearrangement in Cu(hfac)2LEt is unusual; it leads to longer Cu–O distances in the Cu(II)–O•–N< Exchange Cluster and to an abrupt transition from antiferromagnetic to ferromagnetic Exchange. At reduced temperatures, the unit cell volume decreased by 5-6% in all of the compounds. The cell parameters are large and so is the absolute value of the decrease (up to 400 A3). The maximal decrease in the cell dimensions was observed in the directions of the chains and in the directions of the maximal shortening of the Cu...Cu distances. Minimal compression or even extension of the cell took place in the direction of lengthening of the Cu–Ohfac distances. The single crystals of Cu(hfac)2LEt and Cu(hfac)2LPr possess high mechanical stability in repeated cooling-heating cycles.
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The synthesis and magnetic properties of two different water-containing layered polymeric NiII complexes with a 3-imidazoline nitroxide. The low efficiency of Exchange interactions through the OH-bridges of water molecules
Polyhedron, 2001Co-Authors: Victor I. Ovcharenko, Galina V. Romanenko, Renad Z. Sagdeev, A. V. Podoplelov, Kira E. Vostrikova, Vladimir N. IkorskiiAbstract:Abstract The layered polymeric complexes NiL2(H2O)2 (1) and NiL2(H2O)(C3H6O) (2), where L is the stable nitroxide 4-(3′,3′,3′-trifluoromethyl-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl and C3H6O is the acetone molecule, have been synthesized. Polymeric layers in 1 are formed by centrosymmetric NiL2(H2O)2 molecules due to H-bonding of group oxygens with coordinated water of adjacent NiL2(H2O)2 molecules. The synthesis of 1 allowed the completion of the investigation of the magnetic properties of a series of isostructural complexes NiL2(ROH)2, where R is H or the hydrocarbon group, as well as to establish that Exchange interactions in the heterospin Exchange Cluster are essentially weaker than those in the Cluster. Among the complexes with nitroxides, 2 has a unique structure. In 2, paramagnetic ligands are in the cis-position and serve different functions: one L is bidentate and the other is bridging tridentate. The distorted octahedral environment of Ni in 2 is formed in the equatorial plane by the enamineketone O and N atoms of the bidentate L and by O atoms of water molecule and the enamineketone group of the tridentate L. The axial positions are occupied by the enamineketone K of the tridentate L and by the oxygen of adjacent molecule. The bridging tridentate Ls link the [NiL2(H2O)] fragments in infinite chains which are combined in layers by means of H-bonding between coordinated water molecules of one chain and oxygens of the bidentate Ls of an adjacent chain (acetone molecules are positioned between the layers and are H-bonded to the water molecules). In 2, the strong antiferromagnetic Exchange in the fragment results in full coupling of one of the unpaired Ni2+ electrons with the unpaired electron of coordinated group.
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Crystal chemistry of coordination compounds with anionic ligands based on stable nitroxide radicals
Journal of Structural Chemistry, 1993Co-Authors: Galina V. Romanenko, Nina V. Podberezskaya, N. V. PervukhinaAbstract:Due to a recent expansion of research into metal complexes with stable NR connected with prospects for the production of a radically new class of magnetic materials [50, 51], a great amount of data has been accumulated, in particular, on CC with anionic NR ligands. But until recently there were no reviews analyzing the structural features of these compounds. The reason for this is, evidently, dissimilarity of both the NR ligands and the CC based on them. The systematic studies on the synthesis, crystal structures, and magnetic properties of CC with 3-imidazoline NR permitted analysis of the crystallochemical structure of compounds. As the present paper is virtually the first publication that overviews structural studies of CC with NR, we did not undertake to give a complete analysis of the “structure-property” relationship. Nevertheless, the structural data obtained for CC with 3-imidazoline NR allow one to make some correlations between the character of Exchange interactions and the electronic and spatial structure of CC [6, 7, 31]. It is known that to choose an Exchange Cluster model, one needs information on the relative arrangement of PMC. But the quantum-chemical calculations of the electronic states of a system require exact data on the stereochemistry of a coordination unit and mutual arrangement of PMC. Besides, it should be noted that the relationship between crystal symmetry (centrosymmetric or acentric space group) and magnetic properties will not become adequate unitl crystal structure and symmetry studies have been carried out in a magnetic field at appropriate temperatures, i.e., under conditions of measurement of magnetic parameters for compounds of a given class. In the near future, this research will certainly be continued, both in the field of synthesis of CC with 3-imidazoline NR and preparation of their single crystals, and in the field of studies on their structure, magnetic and other physical properties, as well as of quantum-chemical calculations.
