Spin transitions in non-classical systems

Овчаренко, В. И.; Maryunina, Kseniya; Fokin, S. V.; Tretyakov, Evgeny V.; Романенко, Г. В.; Ikorskiǐ, V. N.

doi:10.1007/s11172-005-0136-4

Cited by 97 publications

(147 citation statements)

References 18 publications

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“…One-spin coordination site CuO 4 N 2 demonstrates a rearrangement with changing axial direction of the elongated axis to an equatorial one (Fig. 6) quite similar to the two-spin cluster case 31 of Cu(hfac) 2 L Me . The octahedra CuO 6 remain elongated below the transition temperature T = 220 K. Therefore, according to the GKA rules 36 values J should be positive over whole temperature range.…”

Section: B the Cu(hfac) 2 L Et Casementioning

confidence: 56%

“…GGA+U+J H , GGA+U d +U p , PBE0/def2-TZVP and B3LYP/def2-TZVP reproduce the change of magnetic coupling sign below T = 220 K that is consistent with available magneto-chemical experimental data. 31 The GGA and GGA + U methods also demonstrate similar behavior of magnetic coupling constant, however the transition temperature obtained does not correspond to the experiment. The most inaccurate approach we found is PBE0/6-31G(d).…”

Section: B the Cu(hfac) 2 L Et Casementioning

confidence: 89%

“…1) and exhibits a low-temperature Jahn-Teller structural transition with doubling the chain period. 1, 31 In the case of Cu(hfac) 2 L Et the polymer chain includes three-spin exchange clusters alternating with octahedral coordinated ion Cu 2+ carrying spin 1 /2 (Fig. 5).…”

Section: -mentioning

confidence: 99%

“…For Cu(hfac) 2 L Et compound the calculations were performed with the experimentally measured crystal structure data, presented in Ref. 31.…”

Section: -4mentioning

confidence: 99%

“…The resulting chain consists of alternating sequence of elongated along the chain octahedra and the flattened ones. 31 Table I represents our results for intracluster magnetic coupling constants calculated with different DFT methods above and below the transition temperature. Two numbers in a table cell are magnetic coupling constants for both of these adjacent clusters.…”

Section: A the Cu(hfac) 2 L Me Casementioning

confidence: 99%

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Exchange coupling transformations in Cu (II) heterospin complexes of “breathing crystals” under structural phase transitions

2015

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Family of "breathing crystals" is the polymer-chain complexes of Cu(hfac) 2 with nitroxides. The polymer chains consist of one-, two-or three-spin clusters. The "breathing crystals" experience simultaneous magnetic and Jahn-Teller type structural phase transitions with change of total cluster spin and drastic change of bond lengths (ca. 10-12%). For the first time the intra-cluster magnetic couplings in "breathing crystals" have been calculated both by band structure methods GGA+U and hybrid DFT (B3LYP and PBE0) for the isolated exchange clusters. The temperature dependence of the magnetic coupling constant was calculated for two polymer-chain compounds of the "breathing crystal" family -C 21 H 19 CuF 12 N 4 O 6 with the chains containing two-spin clusters and C 22 H 21 CuF 12 N 4 O 6 with the chains of alternating three-spin clusters and one-spin sites. It was found that adding a Hubbard-like parameter not only to the copper 3d electrons but also to the oxygen 2p electrons (GGA+U d +U p approach) results in an improved description of exchange coupling in the "breathing crystal" compounds. At the same time treatment of the isolated clusters by a large basis hybrid DFT with high computational cost provides a similar quality fit of the experimental magneto-chemical data as that for the GGA+U d +U p band structure calculation scheme. Our calculations also showed that in spite of the abrupt transformation of the magnetic coupling constant under the phase transition, the band gap in the "breathing crystals" remains about the same value with temperature decrease. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

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Section: B the Cu(hfac) 2 L Et Casementioning

confidence: 56%

Section: B the Cu(hfac) 2 L Et Casementioning

confidence: 89%

Section: -mentioning

confidence: 99%

“…For Cu(hfac) 2 L Et compound the calculations were performed with the experimentally measured crystal structure data, presented in Ref. 31.…”

Section: -4mentioning

confidence: 99%

Section: A the Cu(hfac) 2 L Me Casementioning

confidence: 99%

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Exchange coupling transformations in Cu (II) heterospin complexes of “breathing crystals” under structural phase transitions

2015

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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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Breathing Crystals from Copper Nitroxyl Complexes

Овчаренко

Bagryanskaya

2013

Spin‐Crossover Materials

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IntroductionCoordination chemistry of transition metals with stable nitroxides is one of the actively developed branches of modern chemistry which is an important tool in solving the problems of molecular magnetism. The results of studies of metal complexes with nitroxides and their synthesis have been reported from various viewpoints in monographs and reviews. 1-19 Studies of heterospin compounds have led to the creation of new classes of compounds with new combinations of physical characteristics. 19 These include breathing crystals based on Cu(II) coordination compounds with stable nitroxides. Interest in these compounds has recently developed enormously and their number has increased dramatically. This prompted us to summarize data on their magnetostructural correlations. The discussion concentrated on Cu(II) hexafluoroacetylacetonate complexes [Cu(hfac) 2 ] with pyrazolyl-substituted nitronyl nitroxides. These compounds have been studied for more than 10 years 20, 21 and are well defined. The first part of the chapter summarizes the main features of breathing crystals, obtained using X-ray and magnetic measurements, and the second part overviews the results of EPR. EPR spectroscopy as applied to breathing crystals has a number of peculiarities which demands the development of new approaches. EPR study of breathing crystals is very informative, even though the exchange interaction in nitroxide-copper-nitroxide clusters significantly exceeds the value of Zeeman interaction.A very interesting characteristic of the complexes is the similarity of their magnetic properties to spintransitions in classical systems based on the temperature dependence of the effective magnetic moment (μ eff ). Note that the classical spin-crossover 22-35 is absolutely impossible in Cu(II) complexes with diamagnetic ligands, which contain only d 9 paramagnetic centers. The main distinction of spin-transitions in Cu(II) Spin-Crossover Materials: Properties and Applications, First Edition. Edited by Malcolm A. Halcrow.

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Spin transitions in non-classical systems

Cited by 97 publications

References 18 publications

Exchange coupling transformations in Cu (II) heterospin complexes of “breathing crystals” under structural phase transitions

Exchange coupling transformations in Cu (II) heterospin complexes of “breathing crystals” under structural phase transitions

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Breathing Crystals from Copper Nitroxyl Complexes

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