Spin transition in the Cu(hfac)2complex with (4-ethylpyridin-3-yl)-substituted nitronyl nitroxide caused by the “asymmetric” structural rearrangement of exchange clusters in the heterospin molecule

Natalia Artiukhova, Galina Romanenko, Gleb Letyagin, Artem Bogomyakov, Sergey Veber, Olga Minakova, Marina Petrova, Vitaliy Morozov, Victor Ovcharenko

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3 Citations (Scopus)


Methods for the synthesis of binuclear [Cu(hfac)2LEt]2and 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–heating cycles. It was found that a singlet–triplet conversion occurred in all of the {Cu(II)–O•–N<} exchange clusters in the molecules of the binuclear [Cu(hfac)2LEt]2which led to spin coupling with cooling. The transition occurred in a wide temperature range with a maximum gradient ΔχT at ≈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–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 ≈154 K and ≈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 χT(T) curve during the repeated cooling–heating cycles (T½↑ = 122 K, T½↓ = 115 K). This transition is unusual because it causes spin coupling in half of all of the {>N–•O–Cu2+} terminal exchange clusters, leading to spin compensation for only two paramagnetic centers of the six centers in the molecule.

Original languageEnglish
Article number285
Number of pages13
Issue number6
Publication statusPublished - 1 Jun 2019


  • Cu(II) complexes
  • Magnetostructural correlations
  • Nitroxides
  • Phase transitions
  • Spin crossover
  • LN
  • phase transitions
  • spin crossover
  • magnetostructural correlations
  • nitroxides


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