Kira Vostrikova - Academia.edu (original) (raw)
Papers by Kira Vostrikova
A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxa... more A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxazolidine nitroxyl radical were obtained in acetonitrile media starting from nitrates. The compounds, [LnRad(NO3)3] (Ln = Gd, Tb, Dy, Tm, Y; Rad = 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl), have molecular structure. Their coordination polyhedron, LnO7N2, can be described as a tricapped trigonal prism with symmetry close to D3h. The value of 23 cm-1 for the antiferromagnetic coupling Gd-Rad established from the DC magnetic and EPR data is a record strength for the complexes of 4f-elements with nitroxyl radicals. The terbium derivative displays frequency-dependent out-of-phase signals in zero field indicating single-molecule magnetic behavior with an effective barrier of 57 cm-1.
Magnetochemistry
Two novel low-dimensional molecular magnetic materials were prepared by the self-assembly of 3d-a... more Two novel low-dimensional molecular magnetic materials were prepared by the self-assembly of 3d-and 5d-metal complexes. These are the first neutral heterobimetallic cyanobridged compounds involving one anisotropic Mn(III) Schiff base complex and one octacyanotungstate(V) per molecular unit. A slow diffusion of the constituents' solutions leads to the formation of the 0D crystalline complex 1, due to coordination of a water molecule to the Mn center, which prevents polymer formation. A rapid mixing of reagents results in the precipitation of the microcrystalline powder of complex 2, which based on the totality of experimental data, possesses a 1D polymeric structure. The magnetic studies have shown that antiferromagnetic exchange interactions prevail in 1 (J/k B = −13.1(7) K, D = −3.0(1.3) K, zJ' = −0.16(20) K and g av = 2.00(1)); while the presence of the significant intramolecular Mn(III)-W(V) ferromagnetic coupling through cyanide bridge is characteristic for 2 (J/k B = 46.1(5) K, g Mn = 2.11(3), fixed g W = 2.0). Due to the weak interchain interactions, zJ /k B = −0.8(2) K, and compound 2 is a metamagnet with the Néel temperature of 9.5 K undergoing a spin-flip transition at 2 kOe. The slow magnetization dynamics of 2 were investigated at a DC field of 0 and 2 kOe, giving the values of τ 0 32(15) and 36(15) ps, respectively, well within the range typical for single-chain magnets (SCMs). The respective ∆ τ /k B values were 48.4(1.2) and 44.9(1.0) K.
The synthesis of nitronyl and imino nitroxides has been reexamined with the aim of both increasin... more The synthesis of nitronyl and imino nitroxides has been reexamined with the aim of both increasing yields and of offering opportunities for new structures. The conditions for the formation of 2,3-bis(hydroxyamino)-2,3-di-methylbutane, the key intermediate of Ullmans route, have been carefully studied, and a new procedure is proposed , which affords the free base in a very pure form and up to 60 % yield. Full characterization of this intermediate including an X-ray crystal structure is presented. An alternative synthetic route through 2,3-diamino-2,3-dimethyl-butane and the corresponding imida-zolidines which bypasses the delicate synthesis of the bis(hydroxyamino) compound is described. It is shown that 3-chloroperbenzoic acid is an effective oxidant for the transformation of adequately substituted imidazolidines into nitronyl nitroxides, which are obtained in high yield. An illustration of the potentialities of this new route, a new nitronyl nitroxide with two ethyl sub-stituents in positions 4 and 5 of the imidazoline ring, is reported. The scope and limitations of the two routes are discussed.
Sensors and Actuators B: Chemical, 2017
European Journal of Inorganic Chemistry, 2016
Molecular Crystals and Liquid Crystals, 1999
The synthesis, characterisation and magnetic properties of two series of polynuclear cyanide-brid... more The synthesis, characterisation and magnetic properties of two series of polynuclear cyanide-bridged high spin molecules are presented. Tetranuclear compounds of general formula (NC)3M(CNM′L5)3 7H2O (M = Fe, Cr and M′ = Mn, Fe) are obtained by using peripheral complexes with pentadentate ligands. Pentanuclear complexes ((NC)3Cr[CNNi(ligand)2NC]3Cr(CN)3 6H2O) are designed owing to steric hindrance induced by bulky bidentate ligands chelating the peripheral Ni complexes. The magnetic properties show that ground states with spin up to 9 may be obtained.
![Research paper thumbnail of Synthesis and structure of mono- and binuclear copper(II) complexes with polyfunctional nitroxide 4-(1′carboxy-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl, [Cu(LH) 2(H 2O) 2] and [Cu 2L 2(H 2O) 5]. Caterpillar-like reaction](https://attachments.academia-assets.com/48526876/thumbnails/1.jpg)
](Polyhedron, 1997
CuII reacted with the polyfunctional nitroxide 4-(1′-carboxy-2′-oxopropylidene)-2,2,5,5-tetrameth... more CuII reacted with the polyfunctional nitroxide 4-(1′-carboxy-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl (H2L; Cu/H2L = 1:2) to yield Cu(LH)2(H2O)2, which was characterized by strong fixation of water molecules exclusively by hydrogen bonds. In the interaction of Cu(LH)2(H2O)2 with an additional amount of CuII Cu/H2L = 1:1), the ligands noved towards each other in parallel directions to form the binuclear compound Cu2L2(H2O)5. This process is very unusual in coordination chemistry.
Journal of the American Chemical Society, 2003
We report molecular structures and temperature-dependent magnetic susceptibility data for several... more We report molecular structures and temperature-dependent magnetic susceptibility data for several new metal complexes of heterospin triplet ground-state biradical ligands. The ligands are comprised of both nitronyl-nitroxide (NN) and semiquinone (SQ) spin carriers. Five compounds are five-coordinate M(II) complexes (M = Mn, Co, Ni, Cu, and Zn), and one is a six-coordinate Ni(II) complex. Five compounds were structurally characterized. During copper complex formation a reaction with methanol occurs to form a unique methoxy-substituted SQ ring. Variable-temperature magnetic susceptibility studies are consistent with strong intraligand (NN-SQ and NN-PhSQ) ferromagnetic exchange coupling. For the five-coordinate Mn, Co, and Ni complexes, the S = 1 ligand is antiferromagnetically coupled to the metal. For both the five-coordinate Cu complex and the six-coordinate Ni complex, the ligand is ferromagnetically coupled to the metal spins in accordance with orbital symmetry arguments. Despite the low molecular symmetries, the predicted trend in metal-ligand exchange interactions is supported by spin dimer analysis based on extended Hückel calculations. For (NN-SQ)NiTp(Cum,Me)() (Tp(Cum,Me)() = hydro-tris(3-cumenyl-5-methylpyrazolyl)borate), an antisymmetric exchange term was required for the best fit of the magnetic susceptibility data. Antisymmetric exchange was less important for the other complexes due to inherently smaller Deltag. Finally, it is shown that intraligand exchange coupling is of paramount importance in stabilizing high-spin states of mixed metal-biradical complexes.
Journal of the American Chemical Society, Oct 1, 2003
A magnetostructural correlation (conformational electron spin exchange modulation) within an isos... more A magnetostructural correlation (conformational electron spin exchange modulation) within an isostructural series of biradical complexes is presented. X-ray crystal structures, variable-temperature electron paramagnetic resonance spectroscopy, zero-field splitting parameters, and variable-temperature magnetic susceptibility measurements were used to evaluate molecular conformation and electron spin exchange coupling in this series of molecules. Our combined results indicate that the ferromagnetic portion of the exchange couplings occurs via the cross-conjugated pi-systems, while the antiferromagnetic portion occurs through space and is equivalent to incipient bond formation. Thus, molecular conformation controls the relative amounts of ferro- and antiferromagnetic contributions to exchange coupling. In fact, the exchange parameter correlates with average semiquinone ring torsion angles via a Karplus-Conroy-type relation. Because of the natural connection between electron spin exchange coupling and electronic coupling related to electron transfer, we also correlate the exchange parameters in the biradical complexes to mixed valency in the corresponding quinone-semiquinone radical anions. Our results suggest that delocalization in the cross-conjugated, mixed-valent radical anions is proportional to the ferromagnetic contribution to the exchange coupling in the biradical oxidation states.
Coordination Chemistry Reviews, Jul 1, 2008
ABSTRACT This review presents a survey of the literature dedicated to the design of metal complex... more ABSTRACT This review presents a survey of the literature dedicated to the design of metal complexes of stable free radical ligands that have a ground spin state of high multiplicity but excluding extended species. Most stable free radicals have a sophisticated chemistry allowing the design of multi-si te coordination ligands whose metal complexes are oligonuclear with a fairly high ground spin state. The versatile magnetic behavior of these species associated with the direct bonding of metal and organic spin carriers is described. The advantages of using organic free radical ligands for building up single-molecule magnets (SMM) is discussed. © 2007 Elsevier B.V. All rights reserved.
Inorg Chem, 2000
A "spin diverse" S = 3/2 ground-state complex, NN-SQCuTpCum,Me, has been prepar... more A "spin diverse" S = 3/2 ground-state complex, NN-SQCuTpCum,Me, has been prepared. The three S = 1/2 spin carriers are nitronyl nitroxide (NN), o-semiquinone (o-SQ), and cupric ion. The solid-state structure of the ZnII derivative, NN-SQZnTpCum,Me (C56H69BN8O4Zn), was determined: monoclinic, P2(1)/c, a = 12.5781(12) A, b = 17.7408(17) A, c = 24.440(2) A, alpha = 90.00 degrees, beta = 98.240(2) degrees, gamma = 90.00 degrees, Z = 4. The results of X-ray structural characterization of the ZnII derivative suggest substantial interaction between the two spin carriers NN and o-SQ. Indeed, strong intramolecular exchange coupling has been determined by variable-temperature magnetic susceptibility studies. Intraligand ferromagnetic exchange is considerably greater than kT, such that only the triplet state is populated at 300 K, and CuII-ligand exchange is ferromagnetic, with J = +75 cm-1.
Journal of Solid State Chemistry, 2015
ABSTRACT The results of the first steps in the design of coordination polymers based on penta- an... more ABSTRACT The results of the first steps in the design of coordination polymers based on penta- and heptacyanometallates of heavier d transitions metals are presented. The 2D structure of the coordination polymers: [{Mn(acacen)}2Ru(NO)(CN)5]n and two complexes composed of different cyanorhenates, [Ni(cyclam)]2[ReO(OH)(CN)4](ClO4)2(H2O)1.25 and [Cu(cyclam)]2[Re(CN)7](H2O)12, was confirmed by single crystal XRD study, the rhenium oxidation state having been proved by the magnetic measurements. An amorphism of [M(cyclam)]3[Re(CN)7]2 (M=Ni, Cu) polymers does not allow to define strictly their dimensionality and to model anisotropic magnetic behavior of the compounds. However, with high probability a honey-comb like layer structure could be expected for [M(cyclam)]3[Re(CN)7]2 complexes, studied in this work, because such an arrangement is the most common among the bimetallic assemblies of hexa- and octacyanometallates with a ratio [M(cyclam)]/[M(CN)n]=3/2. For the first time was prepared and fully characterized a precursor (n-Bu4N)2[Ru(NO)(CN)5], soluble in organic media.
Coordination Chemistry Reviews, 2008
ABSTRACT This review presents a survey of the literature dedicated to the design of metal complex... more ABSTRACT This review presents a survey of the literature dedicated to the design of metal complexes of stable free radical ligands that have a ground spin state of high multiplicity but excluding extended species. Most stable free radicals have a sophisticated chemistry allowing the design of multi-si te coordination ligands whose metal complexes are oligonuclear with a fairly high ground spin state. The versatile magnetic behavior of these species associated with the direct bonding of metal and organic spin carriers is described. The advantages of using organic free radical ligands for building up single-molecule magnets (SMM) is discussed. © 2007 Elsevier B.V. All rights reserved.
Polyhedron, 2011
ABSTRACT A nitronyl nitroxide, 2-(benzimidazolyl)-4,4,5,5,-tetramethylimidazolidinyl-3-oxide-1-ox... more ABSTRACT A nitronyl nitroxide, 2-(benzimidazolyl)-4,4,5,5,-tetramethylimidazolidinyl-3-oxide-1-oxy, 1 and its imino nitroxide analog 2, have been included in cucurbit[n]urils, CBn (n=7,8), as their hydrochlorides and neutral compounds as well. The hydrochlorides form soluble 1:1 complexes. In the solid state the paramagnetic centers are well isolated and magnetic interactions are cancelled out in contrast to what is observed for the pure nitroxides. The two inclusion complexes involving 1 were characterized by X-ray crystallography. When they were heated in the solid state, one observed a clean conversion of the nitronyl nitroxide guest, 1, into its analog 2.
ChemInform, 2011
ABSTRACT Paramagnetic hexacyanoruthenate(III) and hexacyanoosmate(III), which are interesting bui... more ABSTRACT Paramagnetic hexacyanoruthenate(III) and hexacyanoosmate(III), which are interesting building blocks for designing anisotropic high-spin cluster in relation with single molecule magnets, are easily prepared in high yields by oxidation of the RuII and OsII precursors.
Comptes Rendus de l'Académie des Sciences - Series IIC - Chemistry, 2001
We describe here the synthesis, the magnetic properties, and a comparison of the X-band EPR spect... more We describe here the synthesis, the magnetic properties, and a comparison of the X-band EPR spectra of complexes belonging to the homologous families Ln III (HBPz 3 ) 2 (3,5-DTBSQ) and Ln III (HBPz 3 ) 2 (tropolonate) (where HBPz 3 = hydrotrispyrazolylborate, 3,5-DTBSQ = 3,5-di-tert-butylsemiquinone and Ln = Yb and Ho). This study shows new examples of violations to the rule that ferromagnetic coupling should hold for ions of the second half of the lanthanide series and an unpaired spin. © 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS rare-earth complexes / semiquinonate ligands / tropolonate ligands / X-band EPR / magnetic properties / crystal field / exchange effects Version française abrégée -Champ cristallin et effets d'échange dans des complexes d'ions terre rare et de semiquinones. De par le fait qu'ils possèdent un important moment magnétique anisotrope, les ions lanthanides présentent un grand intérêt dans le domaine du magnétisme moléculaire. Cependant, la présence d'un fort couplage spin-orbite rend l'interprétation des données magnétiques des complexes de Ln(III) difficile, d'autant plus que les ions sont impliqués dans de faibles interactions magnétiques, dont l'intensité est comparable à leur champ cristallin. Une des approches qui ont été utilisées pour obtenir des renseignements sur la nature de l'interaction magnétique au sein de complexes hétérodinucléaires Cu(II)-Ln(III) consiste à éliminer la contribution du champ cristallin de l'ion lanthanide par comparaison des propriétés magnétiques de ce premier système avec celles d'un analogue synthétique diamagnétique . La différence de comportement est alors attribuée aux interactions magnétiques intramoléculaires dans le système Cu(II)-Ln(III). La même approche est utilisée dans ce travail, afin de remonter aux propriétés magnétiques de systèmes appartenant à la famille Ln III (HBPz 3 ) 2 (3,5-DTBSQ), en comparaison avec les complexes Ln III (HBPz 3 ) 2 (tropolonate) (le tropolonate étant un ligand diamagnétique), où HBPz 3 = hydrotrispyrazolylborate, 3,5-DTBSQ = 3,5-di-tert-butylsemiquinone et Ln = Yb et Ho. Les complexes Ln III (HBPz 3 ) 2 (3,5-DTBSQ) cristallisent dans le système monoclinique P2 1 /c et sont isostructuraux au système analogue synthétisé avec l'yttrium, dont la vue Ortep de la structure cristalline, résolue par diffraction des rayons X, est représentée sur la , et 5 montrent, respectivement, les spectres RPE en bande X et à 4,2 K des complexes Ho-semiquinonate, Yb-tropolonate et Yb-semiquinonate. Le complexe Ho-tropolonate ne présente pas de spectre RPE dans ces conditions. La différence entre les spectres RPE de deux complexes synthétisés avec le même ion lanthanide provient de la modification des propriétés magnétiques des systèmes, de par l'existence ou non d'un couplage magnétique intramoléculaire. Les courbes T en fonction de T pour les complexes de Ho(III) et de Yb(III) sont données, respectivement, sur les figures 6 et 7. Dans chaque cas, on trouve à température ambiante la valeur T attendue pour l'ion terre rare seul ou l'ion terre rare plus la semiquinone. Les différences ∆( T) en fonction de T entre complexes dérivés de la même terre rare sont représentées sur la figure 8. Ces deux différences sont constantes entre 100 et 300 K (0,375 emu·K·mol -1 , valeur attendue pour une semiquinone seule), indiquant, en première approximation, que les effets du champ cristallin dans les deux complexes sont identiques. En dessous de 100 K et dans les deux cas, ∆( T) s'éloigne de 0,375 emu·K·mol -1 . Si cette non-monotonie peut s'expliquer essentiellement par des termes d'anisotropie différents dans l'hamiltonien d'échange et par des différences dans l'effet du champ cristallin, plus importants lorsque la température diminue, le comportement complètement différent entre l'holmium(III) et l'ytterbium(III) -deux ions issus de la seconde moitié de la série des lanthanides -vis-à-vis de la semiquinone est encore une violation de la loi selon laquelle est attendu un couplage de nature ferromagnétique entre un ion terre rare de cette moitié de la série et un spin S = 1/2 [19]. D'autres études devront être par la suite réalisées afin de rationaliser les facteurs affectant le couplage magnétique des ions terre rare. © 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS complexes d'ions terre rare / ligands semiquinonate / ligands tropolonate / RPE en bande X / propriétés magnétiques / champ cristallin / effets d'échange
Polyhedron, 1994
... OH-BRIDGES OF WATER MOLECULES VICTOR I. OVCHARENKO,* KIRA E. VOSTRIKOVA, ALEXEI V. PODOPLELOV... more ... OH-BRIDGES OF WATER MOLECULES VICTOR I. OVCHARENKO,* KIRA E. VOSTRIKOVA, ALEXEI V. PODOPLELOV and RENAD Z. SAGDEEV International Tomography Centre, Russian Academy of Sciences, Institutskaya str. 3a, Novosibirsk 630090, Russia and GALINA V ...
Chemical Communications, 2014
The first single chain magnet (SCM) based on orbitally degenerate hexacyanoosmate(III) was prepar... more The first single chain magnet (SCM) based on orbitally degenerate hexacyanoosmate(III) was prepared. The high values of energy barriers for the [Mn(acacen)Os(CN)6](2-) complex of 81 and 48.4 K are the result of interplay of three axes anisotropic coupling of [Os(CN)6](3-) with zero field splitted Mn(3+).
Inorganic chemistry, Jan 6, 2014
Substitution of the organic cation X in the 1D polymer, (X)2[Mn(acacen)Fe(CN)6], leads to an esse... more Substitution of the organic cation X in the 1D polymer, (X)2[Mn(acacen)Fe(CN)6], leads to an essential change in magnetic behavior. Due to the presence of more voluminous Ph4P(+) cations, the polyanion has a more geometrically distorted chain skeleton and, as a consequence, enhanced single chain magnet (SCM) characteristics compared to those for Et4N(+). The Arrhenius relaxation energy barriers, the exchange interaction constant and the zero-field splitting anisotropy of Mn(III) are determined from the analysis of magnetic measurements. The discussion is supported with ligand field calculations for [Fe(CN)6](3-) that unveils the significant anisotropy of Fe magnetic moments.
Inorganic chemistry, Jan 6, 2014
A new highly anisotropic coordination heterobimetallic polymer [Mn(III)(Schiff-base)]3[Re(IV)(CN)... more A new highly anisotropic coordination heterobimetallic polymer [Mn(III)(Schiff-base)]3[Re(IV)(CN)7] was synthesized and characterized structurally and magnetically. The single crystal X-ray analysis has revealed that this is the first framework among the complexes composed of homoleptic cyanometallate and Mn(III) complex of the tetradentate Schiff base ligand. A formation of 3D assembly is possible due to both the pentagonal bipyrimidal geometry of the cyanometallate unit and suitable size of constituents: [Re(CN)7](3-) and [Mn(III)(acacen)](+), where acacen = N,N'-ethylenebis(acetylacetoneiminato). The powder and crystal magnetic studies show that the compound undergoes an antiferromagnetic ordering of a complicated character below Neel temperature of 13 K, and exhibits a metamagnetic behavior and strong magnetic anisotropy similar to those observed in related 3D Mn(II)-[Mo(CN)7](4-) systems. Unusual magnetic properties of [Mn(III)(acacen)]3[Re(IV)(CN)7] (1) originate from an i...
A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxa... more A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxazolidine nitroxyl radical were obtained in acetonitrile media starting from nitrates. The compounds, [LnRad(NO3)3] (Ln = Gd, Tb, Dy, Tm, Y; Rad = 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl), have molecular structure. Their coordination polyhedron, LnO7N2, can be described as a tricapped trigonal prism with symmetry close to D3h. The value of 23 cm-1 for the antiferromagnetic coupling Gd-Rad established from the DC magnetic and EPR data is a record strength for the complexes of 4f-elements with nitroxyl radicals. The terbium derivative displays frequency-dependent out-of-phase signals in zero field indicating single-molecule magnetic behavior with an effective barrier of 57 cm-1.
Magnetochemistry
Two novel low-dimensional molecular magnetic materials were prepared by the self-assembly of 3d-a... more Two novel low-dimensional molecular magnetic materials were prepared by the self-assembly of 3d-and 5d-metal complexes. These are the first neutral heterobimetallic cyanobridged compounds involving one anisotropic Mn(III) Schiff base complex and one octacyanotungstate(V) per molecular unit. A slow diffusion of the constituents' solutions leads to the formation of the 0D crystalline complex 1, due to coordination of a water molecule to the Mn center, which prevents polymer formation. A rapid mixing of reagents results in the precipitation of the microcrystalline powder of complex 2, which based on the totality of experimental data, possesses a 1D polymeric structure. The magnetic studies have shown that antiferromagnetic exchange interactions prevail in 1 (J/k B = −13.1(7) K, D = −3.0(1.3) K, zJ' = −0.16(20) K and g av = 2.00(1)); while the presence of the significant intramolecular Mn(III)-W(V) ferromagnetic coupling through cyanide bridge is characteristic for 2 (J/k B = 46.1(5) K, g Mn = 2.11(3), fixed g W = 2.0). Due to the weak interchain interactions, zJ /k B = −0.8(2) K, and compound 2 is a metamagnet with the Néel temperature of 9.5 K undergoing a spin-flip transition at 2 kOe. The slow magnetization dynamics of 2 were investigated at a DC field of 0 and 2 kOe, giving the values of τ 0 32(15) and 36(15) ps, respectively, well within the range typical for single-chain magnets (SCMs). The respective ∆ τ /k B values were 48.4(1.2) and 44.9(1.0) K.
The synthesis of nitronyl and imino nitroxides has been reexamined with the aim of both increasin... more The synthesis of nitronyl and imino nitroxides has been reexamined with the aim of both increasing yields and of offering opportunities for new structures. The conditions for the formation of 2,3-bis(hydroxyamino)-2,3-di-methylbutane, the key intermediate of Ullmans route, have been carefully studied, and a new procedure is proposed , which affords the free base in a very pure form and up to 60 % yield. Full characterization of this intermediate including an X-ray crystal structure is presented. An alternative synthetic route through 2,3-diamino-2,3-dimethyl-butane and the corresponding imida-zolidines which bypasses the delicate synthesis of the bis(hydroxyamino) compound is described. It is shown that 3-chloroperbenzoic acid is an effective oxidant for the transformation of adequately substituted imidazolidines into nitronyl nitroxides, which are obtained in high yield. An illustration of the potentialities of this new route, a new nitronyl nitroxide with two ethyl sub-stituents in positions 4 and 5 of the imidazoline ring, is reported. The scope and limitations of the two routes are discussed.
Sensors and Actuators B: Chemical, 2017
European Journal of Inorganic Chemistry, 2016
Molecular Crystals and Liquid Crystals, 1999
The synthesis, characterisation and magnetic properties of two series of polynuclear cyanide-brid... more The synthesis, characterisation and magnetic properties of two series of polynuclear cyanide-bridged high spin molecules are presented. Tetranuclear compounds of general formula (NC)3M(CNM′L5)3 7H2O (M = Fe, Cr and M′ = Mn, Fe) are obtained by using peripheral complexes with pentadentate ligands. Pentanuclear complexes ((NC)3Cr[CNNi(ligand)2NC]3Cr(CN)3 6H2O) are designed owing to steric hindrance induced by bulky bidentate ligands chelating the peripheral Ni complexes. The magnetic properties show that ground states with spin up to 9 may be obtained.
Polyhedron, 1997
CuII reacted with the polyfunctional nitroxide 4-(1′-carboxy-2′-oxopropylidene)-2,2,5,5-tetrameth... more CuII reacted with the polyfunctional nitroxide 4-(1′-carboxy-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl (H2L; Cu/H2L = 1:2) to yield Cu(LH)2(H2O)2, which was characterized by strong fixation of water molecules exclusively by hydrogen bonds. In the interaction of Cu(LH)2(H2O)2 with an additional amount of CuII Cu/H2L = 1:1), the ligands noved towards each other in parallel directions to form the binuclear compound Cu2L2(H2O)5. This process is very unusual in coordination chemistry.
Journal of the American Chemical Society, 2003
We report molecular structures and temperature-dependent magnetic susceptibility data for several... more We report molecular structures and temperature-dependent magnetic susceptibility data for several new metal complexes of heterospin triplet ground-state biradical ligands. The ligands are comprised of both nitronyl-nitroxide (NN) and semiquinone (SQ) spin carriers. Five compounds are five-coordinate M(II) complexes (M = Mn, Co, Ni, Cu, and Zn), and one is a six-coordinate Ni(II) complex. Five compounds were structurally characterized. During copper complex formation a reaction with methanol occurs to form a unique methoxy-substituted SQ ring. Variable-temperature magnetic susceptibility studies are consistent with strong intraligand (NN-SQ and NN-PhSQ) ferromagnetic exchange coupling. For the five-coordinate Mn, Co, and Ni complexes, the S = 1 ligand is antiferromagnetically coupled to the metal. For both the five-coordinate Cu complex and the six-coordinate Ni complex, the ligand is ferromagnetically coupled to the metal spins in accordance with orbital symmetry arguments. Despite the low molecular symmetries, the predicted trend in metal-ligand exchange interactions is supported by spin dimer analysis based on extended Hückel calculations. For (NN-SQ)NiTp(Cum,Me)() (Tp(Cum,Me)() = hydro-tris(3-cumenyl-5-methylpyrazolyl)borate), an antisymmetric exchange term was required for the best fit of the magnetic susceptibility data. Antisymmetric exchange was less important for the other complexes due to inherently smaller Deltag. Finally, it is shown that intraligand exchange coupling is of paramount importance in stabilizing high-spin states of mixed metal-biradical complexes.
Journal of the American Chemical Society, Oct 1, 2003
A magnetostructural correlation (conformational electron spin exchange modulation) within an isos... more A magnetostructural correlation (conformational electron spin exchange modulation) within an isostructural series of biradical complexes is presented. X-ray crystal structures, variable-temperature electron paramagnetic resonance spectroscopy, zero-field splitting parameters, and variable-temperature magnetic susceptibility measurements were used to evaluate molecular conformation and electron spin exchange coupling in this series of molecules. Our combined results indicate that the ferromagnetic portion of the exchange couplings occurs via the cross-conjugated pi-systems, while the antiferromagnetic portion occurs through space and is equivalent to incipient bond formation. Thus, molecular conformation controls the relative amounts of ferro- and antiferromagnetic contributions to exchange coupling. In fact, the exchange parameter correlates with average semiquinone ring torsion angles via a Karplus-Conroy-type relation. Because of the natural connection between electron spin exchange coupling and electronic coupling related to electron transfer, we also correlate the exchange parameters in the biradical complexes to mixed valency in the corresponding quinone-semiquinone radical anions. Our results suggest that delocalization in the cross-conjugated, mixed-valent radical anions is proportional to the ferromagnetic contribution to the exchange coupling in the biradical oxidation states.
Coordination Chemistry Reviews, Jul 1, 2008
ABSTRACT This review presents a survey of the literature dedicated to the design of metal complex... more ABSTRACT This review presents a survey of the literature dedicated to the design of metal complexes of stable free radical ligands that have a ground spin state of high multiplicity but excluding extended species. Most stable free radicals have a sophisticated chemistry allowing the design of multi-si te coordination ligands whose metal complexes are oligonuclear with a fairly high ground spin state. The versatile magnetic behavior of these species associated with the direct bonding of metal and organic spin carriers is described. The advantages of using organic free radical ligands for building up single-molecule magnets (SMM) is discussed. © 2007 Elsevier B.V. All rights reserved.
Inorg Chem, 2000
A "spin diverse" S = 3/2 ground-state complex, NN-SQCuTpCum,Me, has been prepar... more A "spin diverse" S = 3/2 ground-state complex, NN-SQCuTpCum,Me, has been prepared. The three S = 1/2 spin carriers are nitronyl nitroxide (NN), o-semiquinone (o-SQ), and cupric ion. The solid-state structure of the ZnII derivative, NN-SQZnTpCum,Me (C56H69BN8O4Zn), was determined: monoclinic, P2(1)/c, a = 12.5781(12) A, b = 17.7408(17) A, c = 24.440(2) A, alpha = 90.00 degrees, beta = 98.240(2) degrees, gamma = 90.00 degrees, Z = 4. The results of X-ray structural characterization of the ZnII derivative suggest substantial interaction between the two spin carriers NN and o-SQ. Indeed, strong intramolecular exchange coupling has been determined by variable-temperature magnetic susceptibility studies. Intraligand ferromagnetic exchange is considerably greater than kT, such that only the triplet state is populated at 300 K, and CuII-ligand exchange is ferromagnetic, with J = +75 cm-1.
Journal of Solid State Chemistry, 2015
ABSTRACT The results of the first steps in the design of coordination polymers based on penta- an... more ABSTRACT The results of the first steps in the design of coordination polymers based on penta- and heptacyanometallates of heavier d transitions metals are presented. The 2D structure of the coordination polymers: [{Mn(acacen)}2Ru(NO)(CN)5]n and two complexes composed of different cyanorhenates, [Ni(cyclam)]2[ReO(OH)(CN)4](ClO4)2(H2O)1.25 and [Cu(cyclam)]2[Re(CN)7](H2O)12, was confirmed by single crystal XRD study, the rhenium oxidation state having been proved by the magnetic measurements. An amorphism of [M(cyclam)]3[Re(CN)7]2 (M=Ni, Cu) polymers does not allow to define strictly their dimensionality and to model anisotropic magnetic behavior of the compounds. However, with high probability a honey-comb like layer structure could be expected for [M(cyclam)]3[Re(CN)7]2 complexes, studied in this work, because such an arrangement is the most common among the bimetallic assemblies of hexa- and octacyanometallates with a ratio [M(cyclam)]/[M(CN)n]=3/2. For the first time was prepared and fully characterized a precursor (n-Bu4N)2[Ru(NO)(CN)5], soluble in organic media.
Coordination Chemistry Reviews, 2008
ABSTRACT This review presents a survey of the literature dedicated to the design of metal complex... more ABSTRACT This review presents a survey of the literature dedicated to the design of metal complexes of stable free radical ligands that have a ground spin state of high multiplicity but excluding extended species. Most stable free radicals have a sophisticated chemistry allowing the design of multi-si te coordination ligands whose metal complexes are oligonuclear with a fairly high ground spin state. The versatile magnetic behavior of these species associated with the direct bonding of metal and organic spin carriers is described. The advantages of using organic free radical ligands for building up single-molecule magnets (SMM) is discussed. © 2007 Elsevier B.V. All rights reserved.
Polyhedron, 2011
ABSTRACT A nitronyl nitroxide, 2-(benzimidazolyl)-4,4,5,5,-tetramethylimidazolidinyl-3-oxide-1-ox... more ABSTRACT A nitronyl nitroxide, 2-(benzimidazolyl)-4,4,5,5,-tetramethylimidazolidinyl-3-oxide-1-oxy, 1 and its imino nitroxide analog 2, have been included in cucurbit[n]urils, CBn (n=7,8), as their hydrochlorides and neutral compounds as well. The hydrochlorides form soluble 1:1 complexes. In the solid state the paramagnetic centers are well isolated and magnetic interactions are cancelled out in contrast to what is observed for the pure nitroxides. The two inclusion complexes involving 1 were characterized by X-ray crystallography. When they were heated in the solid state, one observed a clean conversion of the nitronyl nitroxide guest, 1, into its analog 2.
ChemInform, 2011
ABSTRACT Paramagnetic hexacyanoruthenate(III) and hexacyanoosmate(III), which are interesting bui... more ABSTRACT Paramagnetic hexacyanoruthenate(III) and hexacyanoosmate(III), which are interesting building blocks for designing anisotropic high-spin cluster in relation with single molecule magnets, are easily prepared in high yields by oxidation of the RuII and OsII precursors.
Comptes Rendus de l'Académie des Sciences - Series IIC - Chemistry, 2001
We describe here the synthesis, the magnetic properties, and a comparison of the X-band EPR spect... more We describe here the synthesis, the magnetic properties, and a comparison of the X-band EPR spectra of complexes belonging to the homologous families Ln III (HBPz 3 ) 2 (3,5-DTBSQ) and Ln III (HBPz 3 ) 2 (tropolonate) (where HBPz 3 = hydrotrispyrazolylborate, 3,5-DTBSQ = 3,5-di-tert-butylsemiquinone and Ln = Yb and Ho). This study shows new examples of violations to the rule that ferromagnetic coupling should hold for ions of the second half of the lanthanide series and an unpaired spin. © 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS rare-earth complexes / semiquinonate ligands / tropolonate ligands / X-band EPR / magnetic properties / crystal field / exchange effects Version française abrégée -Champ cristallin et effets d'échange dans des complexes d'ions terre rare et de semiquinones. De par le fait qu'ils possèdent un important moment magnétique anisotrope, les ions lanthanides présentent un grand intérêt dans le domaine du magnétisme moléculaire. Cependant, la présence d'un fort couplage spin-orbite rend l'interprétation des données magnétiques des complexes de Ln(III) difficile, d'autant plus que les ions sont impliqués dans de faibles interactions magnétiques, dont l'intensité est comparable à leur champ cristallin. Une des approches qui ont été utilisées pour obtenir des renseignements sur la nature de l'interaction magnétique au sein de complexes hétérodinucléaires Cu(II)-Ln(III) consiste à éliminer la contribution du champ cristallin de l'ion lanthanide par comparaison des propriétés magnétiques de ce premier système avec celles d'un analogue synthétique diamagnétique . La différence de comportement est alors attribuée aux interactions magnétiques intramoléculaires dans le système Cu(II)-Ln(III). La même approche est utilisée dans ce travail, afin de remonter aux propriétés magnétiques de systèmes appartenant à la famille Ln III (HBPz 3 ) 2 (3,5-DTBSQ), en comparaison avec les complexes Ln III (HBPz 3 ) 2 (tropolonate) (le tropolonate étant un ligand diamagnétique), où HBPz 3 = hydrotrispyrazolylborate, 3,5-DTBSQ = 3,5-di-tert-butylsemiquinone et Ln = Yb et Ho. Les complexes Ln III (HBPz 3 ) 2 (3,5-DTBSQ) cristallisent dans le système monoclinique P2 1 /c et sont isostructuraux au système analogue synthétisé avec l'yttrium, dont la vue Ortep de la structure cristalline, résolue par diffraction des rayons X, est représentée sur la , et 5 montrent, respectivement, les spectres RPE en bande X et à 4,2 K des complexes Ho-semiquinonate, Yb-tropolonate et Yb-semiquinonate. Le complexe Ho-tropolonate ne présente pas de spectre RPE dans ces conditions. La différence entre les spectres RPE de deux complexes synthétisés avec le même ion lanthanide provient de la modification des propriétés magnétiques des systèmes, de par l'existence ou non d'un couplage magnétique intramoléculaire. Les courbes T en fonction de T pour les complexes de Ho(III) et de Yb(III) sont données, respectivement, sur les figures 6 et 7. Dans chaque cas, on trouve à température ambiante la valeur T attendue pour l'ion terre rare seul ou l'ion terre rare plus la semiquinone. Les différences ∆( T) en fonction de T entre complexes dérivés de la même terre rare sont représentées sur la figure 8. Ces deux différences sont constantes entre 100 et 300 K (0,375 emu·K·mol -1 , valeur attendue pour une semiquinone seule), indiquant, en première approximation, que les effets du champ cristallin dans les deux complexes sont identiques. En dessous de 100 K et dans les deux cas, ∆( T) s'éloigne de 0,375 emu·K·mol -1 . Si cette non-monotonie peut s'expliquer essentiellement par des termes d'anisotropie différents dans l'hamiltonien d'échange et par des différences dans l'effet du champ cristallin, plus importants lorsque la température diminue, le comportement complètement différent entre l'holmium(III) et l'ytterbium(III) -deux ions issus de la seconde moitié de la série des lanthanides -vis-à-vis de la semiquinone est encore une violation de la loi selon laquelle est attendu un couplage de nature ferromagnétique entre un ion terre rare de cette moitié de la série et un spin S = 1/2 [19]. D'autres études devront être par la suite réalisées afin de rationaliser les facteurs affectant le couplage magnétique des ions terre rare. © 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS complexes d'ions terre rare / ligands semiquinonate / ligands tropolonate / RPE en bande X / propriétés magnétiques / champ cristallin / effets d'échange
Polyhedron, 1994
... OH-BRIDGES OF WATER MOLECULES VICTOR I. OVCHARENKO,* KIRA E. VOSTRIKOVA, ALEXEI V. PODOPLELOV... more ... OH-BRIDGES OF WATER MOLECULES VICTOR I. OVCHARENKO,* KIRA E. VOSTRIKOVA, ALEXEI V. PODOPLELOV and RENAD Z. SAGDEEV International Tomography Centre, Russian Academy of Sciences, Institutskaya str. 3a, Novosibirsk 630090, Russia and GALINA V ...
Chemical Communications, 2014
The first single chain magnet (SCM) based on orbitally degenerate hexacyanoosmate(III) was prepar... more The first single chain magnet (SCM) based on orbitally degenerate hexacyanoosmate(III) was prepared. The high values of energy barriers for the [Mn(acacen)Os(CN)6](2-) complex of 81 and 48.4 K are the result of interplay of three axes anisotropic coupling of [Os(CN)6](3-) with zero field splitted Mn(3+).
Inorganic chemistry, Jan 6, 2014
Substitution of the organic cation X in the 1D polymer, (X)2[Mn(acacen)Fe(CN)6], leads to an esse... more Substitution of the organic cation X in the 1D polymer, (X)2[Mn(acacen)Fe(CN)6], leads to an essential change in magnetic behavior. Due to the presence of more voluminous Ph4P(+) cations, the polyanion has a more geometrically distorted chain skeleton and, as a consequence, enhanced single chain magnet (SCM) characteristics compared to those for Et4N(+). The Arrhenius relaxation energy barriers, the exchange interaction constant and the zero-field splitting anisotropy of Mn(III) are determined from the analysis of magnetic measurements. The discussion is supported with ligand field calculations for [Fe(CN)6](3-) that unveils the significant anisotropy of Fe magnetic moments.
Inorganic chemistry, Jan 6, 2014
A new highly anisotropic coordination heterobimetallic polymer [Mn(III)(Schiff-base)]3[Re(IV)(CN)... more A new highly anisotropic coordination heterobimetallic polymer [Mn(III)(Schiff-base)]3[Re(IV)(CN)7] was synthesized and characterized structurally and magnetically. The single crystal X-ray analysis has revealed that this is the first framework among the complexes composed of homoleptic cyanometallate and Mn(III) complex of the tetradentate Schiff base ligand. A formation of 3D assembly is possible due to both the pentagonal bipyrimidal geometry of the cyanometallate unit and suitable size of constituents: [Re(CN)7](3-) and [Mn(III)(acacen)](+), where acacen = N,N'-ethylenebis(acetylacetoneiminato). The powder and crystal magnetic studies show that the compound undergoes an antiferromagnetic ordering of a complicated character below Neel temperature of 13 K, and exhibits a metamagnetic behavior and strong magnetic anisotropy similar to those observed in related 3D Mn(II)-[Mo(CN)7](4-) systems. Unusual magnetic properties of [Mn(III)(acacen)]3[Re(IV)(CN)7] (1) originate from an i...