C(sp2)-coupled nitronyl nitroxide and iminonitroxide diradicals

Svyatoslav Tolstikov, Evgeny Tretyakov, Sergey Fokin, Elizaveta Suturina, Galina Romanenko, Artem Bogomyakov, Dmitri Stass, Alexander Maryasov, Matvey Fedin, Nina Gritsan, Victor Ovcharenko

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12 Citations (Scopus)

Abstract

Spin-labelled compounds are widely used in chemistry, physics, biology and the materials sciences but the synthesis of stable high-spin organic molecules is still a challenge. We succeeded in synthesising heteroatom analogues of the 1,1,2,3,3-pentamethylenepropane (PMP) diradicals with two nitronyl nitroxide (DR1) and with two iminonitroxide (DR2) fragments linked through the C(sp2) atom of the nitrone group. According to magnetic susceptibility measurements, EPR data and ab initio calculations at the (8,6)CASSCF and (8,6)NEVPT2 levels, DR1 and DR2 have singlet ground states. The singlet-triplet energy splitting (2J) is low (J/k=-7.4 for DR1 and -6.0K for DR2), which comes from the disjoint nature of these diradicals. The reaction of [Cu(hfac)2] with DR1 gives rise to different heterospin complexes in which the diradical acts as a rigid ligand, retaining its initial conformation. For the [{Cu(hfac)2}2(DR1)(H2O)] complex, sufficiently strong ferromagnetic interactions (J1/k=42.7 and J 2/k=14.1K) between two coordinating CuII ions and DR 1 were revealed. In [{Cu(hfac)2}2(DR 1)(H2O)][Cu(hfac)2(H2O)], the very strong and antiferromagnetic (J/k=-416.1K) exchange interaction between one of the coordinating CuII ions and DR1 is caused by the very short equatorial Cuï-O bond length (1.962Å). Playing with spins: New C(sp2)-spaced nitronyl nitroxide and iminonitroxide diradicals are reported. The exciting feature of these diradicals inherent in their nature is the very low singlet-triplet energy splitting. A small difference in the structure of Cu(hfac)2 complexes with the nitronyl nitroxide diradical gives rise to essentially different exchange interactions between the copper and nitroxide spins (see scheme; hfac=hexafluoroacetylacetonate).

Original languageEnglish
Pages (from-to)2793-2803
Number of pages11
JournalChemistry - A European Journal
Volume20
Issue number10
Early online date19 Feb 2014
DOIs
Publication statusPublished - 3 Mar 2014

Keywords

  • EPR spectroscopy
  • heterospin complexes
  • nitroxides
  • quantum chemistry
  • singlet diradicals
  • X-ray diffraction

ASJC Scopus subject areas

  • Chemistry(all)

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    Tolstikov, S., Tretyakov, E., Fokin, S., Suturina, E., Romanenko, G., Bogomyakov, A., Stass, D., Maryasov, A., Fedin, M., Gritsan, N., & Ovcharenko, V. (2014). C(sp2)-coupled nitronyl nitroxide and iminonitroxide diradicals. Chemistry - A European Journal, 20(10), 2793-2803. https://doi.org/10.1002/chem.201302681