Spin Transition in the Cu(hfac)2 Complex with (4-Ethylpyridin-3-yl)-Substituted Nitronyl Nitroxide Caused by the 'Asymmetric' Structural Rearrangement of Exchange Clusters in the Heterospin Molecule
| Autor: | Galina V. Romanenko, Olga Minakova, N. A. Artiukhova, Vitaliy Morozov, V. I. Ovcharenko, Gleb Letyagin, Marina V. Petrova, Artem S. Bogomyakov, Sergey L. Veber |
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| Rok vydání: | 2019 |
| Předmět: |
Phase transition
Nitroxide mediated radical polymerization Materials science General Chemical Engineering Spin transition chemistry.chemical_element 010402 general chemistry 01 natural sciences Inorganic Chemistry Paramagnetism spin crossover nitroxides Spin crossover lcsh:QD901-999 Molecule General Materials Science Spin (physics) Cu(II) complexes magnetostructural correlations 010405 organic chemistry Condensed Matter Physics Copper phase transitions 0104 chemical sciences Crystallography chemistry lcsh:Crystallography |
| Zdroj: | Crystals Volume 9 Issue 6 Crystals, Vol 9, Iss 6, p 285 (2019) |
| ISSN: | 2073-4352 |
| DOI: | 10.3390/cryst9060285 |
| Popis: | Methods for the synthesis of binuclear [Cu(hfac)2LEt]2 and tetranuclear [[Cu(hfac)2]4(LEt)2] heterospin compounds based on copper hexafluoroacetylacetonate [Cu(hfac)2] and 2-(4-ethylpyridin-3-yl)-4,5-bis(spirocyclopentyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt), were developed. The crystals of the complexes are elastic and do not crash during repeated cooling&ndash heating cycles. It was found that a singlet&ndash triplet conversion occurred in all of the {Cu(II)&ndash O&bull &ndash N< } exchange clusters in the molecules of the binuclear [Cu(hfac)2LEt]2 which led to spin coupling with cooling. The transition occurred in a wide temperature range with a maximum gradient &Delta &chi T at &asymp 180 K. The structural transformation of the crystals takes place at T < 200 K and is accompanied by the lowering of symmetry from monoclinic to triclinic, twinning, and a considerable shortening of the Cu&ndash ONO distance (2.19 and 1.97 Å at 295 and 50 K, respectively). For the tetranuclear [[Cu(hfac)2]4(LEt)2], two structural transitions were recorded (at &asymp 154 K and &asymp 118 K), which led to a considerable change in the spatial position of the Et substituent in the nitronyl nitroxyl fragment. The low-temperature process was accompanied by a spin transition recorded as a hysteresis loop on the &chi T(T) curve during the repeated cooling&ndash heating cycles (T½ &uarr = 122 K, T½ &darr = 115 K). This transition is unusual because it causes spin coupling in half of all of the {> N&ndash &bull O&ndash Cu2+} terminal exchange clusters, leading to spin compensation for only two paramagnetic centers of the six centers in the molecule. |
| Databáze: | OpenAIRE |
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