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Овчаренко, В. И.; Fokin, S. V.; Романенко, Г. В.; Shvedenkov, Yu. G.; Ikorskiǐ, V. N.; Tretyakov, Evgeny V.; Василевский, С. Ф.

doi:10.1023/a:1016094421024

Cited by 77 publications

(93 citation statements)

References 8 publications

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“…As a result, a family of heterospin complexes with magnetic properties similar to spin crossover was created. 215,216 The single crystals generally did not crack after the temperature range of the structural transition and the ensuing magnetic transition. The structure was determined for all heterospin complexes and their solid solutions at temperatures before and after the magnetic transition, which provided a unique opportunity for the observation of structure dynamics in the range of the phase transition for these systems.…”

Section: Breathing Crystalsmentioning

confidence: 99%

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Овчаренко¹

2010

Stable Radicals

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IntroductionInteractions between the paramagnetic ions of transition metals and stable radicals are convenient and effective methods for the synthesis of multispin molecules. These metal-nitroxide systems are often called heterospin systems because they contain paramagnetic centers with both d (or f) odd electrons and centers with p electrons. Paramagnetic centers can differ in the electron spin, g factor, the character of electron spin density delocalization, and heat capacity. The presence of several paramagnetic centers in heterospin molecules has stirred growing interest in their magnetic properties because these compounds are convenient objects for studying the subtle peculiarities of exchange interactions and revealing valuable magnetostructural correlations. That is why coordination chemistry of transition metals with stable nitroxides is an actively developing direction in modern chemistry that contributes to problem solving in the field of molecular magnetism. The results of studies on the synthesis and properties of metal complexes with nitroxides have been considered from different viewpoints and at different times in many monographs and reviews. 1 -19 Importantly, this approach offers the potential for control over the structure of the designed heterospin molecule and the character of interactions between the odd electrons of paramagnetic centers, which is necessary for constructing justifiable magnetostructural correlations. This is one of the factors responsible for the continuous growth of the number of new metal-nitroxide complexes. The Cambridge Structural Database alone contains more than one thousand structurally defined metal-nitroxide systems. 20 Therefore, currently it is impossible and not necessary to collect all available literature data on the synthesis and properties of metal-nitroxide systems in one publication. In any account, a comprehensive review of this kind will already have become incomplete by the time of its publication because new heterospin compounds based on transition metal compounds with nitroxides are being added daily to the list. However, the Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron CompoundsEdited by Robin G. Hicks

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Section: Breathing Crystalsmentioning

confidence: 99%

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Овчаренко¹

2010

Stable Radicals

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“…1,2 The systems containing no iron but including, for example, Cu atoms and nitroxy radicals are also known. 3 The energy of low spin states of the centers is usually lower than that of the high spin states and, hence, the fraction of the low spin states increases with the temperature decrease. The geometry of the low spin and high spin centers is differ ent and, therefore, strains accelerating the conversion of the high spin to low spin states increase with an increase in the fraction of the low spin states in the samples, and the phase transition occurs at some temperature.…”

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confidence: 99%

Spin crossover in polyaniline

et al. 2007

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Solutions of the basic form of polyaniline in m cresol were studied by ESR and optical spectroscopy in the visible region. m Cresol can slowly (during one month) protonate polyaniline. For the first time characteristic features of spin crossover were found: sharp changes in the magnetic susceptibility and the ESR line width of polyaniline at ~200 and 250 K, a smooth decrease in the susceptibility and absorption with the temperature increase from 293 to 423 K, and the temperature hysteresis. The temperature induced structural rear rangements of polyaniline are caused, most likely, by singlet triplet transitions in relatively short sections of the polymer chain. The model of short sections permits to explain the origin of the temperature independent part of susceptibility. Quantum chemical calculations for the aniline dimers and tetramers describe correctly the singlet triplet splitting value, thermo chromism, and HFS constants in the spectrum of polyaniline.The term "spin crossover" (SC) or "spin transition" is used for the description of characteristic phenomena in samples, where transitions between the high and low spin states of the centers of the sample occur upon the temperature change or under pressure or irradiation and lead to the structural rearrangement of the sample.Most systems manifesting SC contain iron(II). 1,2 The systems containing no iron but including, for example, Cu atoms and nitroxy radicals are also known. 3 The energy of low spin states of the centers is usually lower than that of the high spin states and, hence, the fraction of the low spin states increases with the temperature decrease. The geometry of the low spin and high spin centers is differ ent and, therefore, strains accelerating the conversion of the high spin to low spin states increase with an increase in the fraction of the low spin states in the samples, and the phase transition occurs at some temperature. The sharpness of the transition is determined by the degree of cooperativity of the system and, as a rule, the temperature hysteresis is observed. Investigation of the nature of this phenomenon, including establishing conditions for the appearance of cooperativity and the mechanism of an irradiation effect and search for new systems manifest ing SC is the matter of numerous studies. The high sensi tivity of parameters of the systems under study, especially absorption in the visible region and magnetic susceptibil ity, to slight changes in the temperature, pressure, and irradiation makes it possible to use them as sensors, dis plays, and information storage devices. To increase the sharpness of the transition, the centers are bound through ligands into polymer structures; however, no true poly mers exhibiting SC are known. The SC term is applied to both solid state systems with sharp temperature induced transitions and solutions with smooth transitions reflect ing the change in the Boltzmann populations of spin states. The systems manifesting SC are rather few, because they need to fulfill several conditions; in particular, t...

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“…For the biradical molecules, the choice of n in the -(CH 2 ) n group necessary for the cross linking of these chains was based on the available structural data for chain polymers of Cu(hfac) 2 with 1 alkylpyrazol 4 yl substituted nitronyl nitroxides. [1][2][3][4] The structural modeling showed that strong structural distortions and strains should appear in both head to head and head to tail polymer chains upon their cross linking by polymethylene bridges, in which the number of methylene units between the pyrazole fragments is ≤4. At the same time, according to the results of structural mod eling, the presence of more then eight methylene units in the -(CH 2 ) n -fragment is excessive and can cause their unpredictable twisting.…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4][5] In the solid state, these complexes exist as heterospin 1D head to head or head to tail polymers formed through the bridging coordina tion of L R with the involvement of the O atom of one >N-O group and the N atom of the pyrazole ring.…”

mentioning

confidence: 99%

Shift of stereochemical nonrigidity from coordination units to polymethylene fragments in heterospin copper(II) hexafluoroacetylacetonate complexes with nitronyl nitroxide biradicals

et al. 2007

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The reactions of bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac) 2 ] with the nitronyl nitroxide biradicals bis[4 (4,4,5,5 tetramethyl 3 oxide 1 oxyl 4,5 dihydro 1H imidazol 2 yl)pyrazol 1 yl]alkanes (L 6 , L 10 , and L 12 ) produced the framework heterospin com plex [Cu(hfac) 2 ] 2 L 6 and the layer polymeric heterospin complexes [Cu(hfac) 2 ] 2 L 10 and {[Cu(hfac) 2 ] 2 L 12 }[Cu(hfac) 2 (Pr i OH) 2 ], respectively. In the solid state of these compounds, the stereochemical nonrigidity is manifested as a deformation of the polymethylene frag ments -(CH 2 ) n -.

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Cited by 77 publications

References 8 publications

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Spin crossover in polyaniline

Shift of stereochemical nonrigidity from coordination units to polymethylene fragments in heterospin copper(II) hexafluoroacetylacetonate complexes with nitronyl nitroxide biradicals

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