High-spin s = 2 ground state aminyl tetraradicals

Andrzej Rajca, Arnon Olankitwanit, Ying Wang, Przemysław J. Boratyński, Maren Pink, Suchada Rajca

Research output: Contribution to journalArticle

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Abstract

Aminyl tetraradicals with planar tetraazanonacene backbones have quintet (S = 2) ground states and do not show any detectable thermal population of the low-spin excited states up to the highest temperature investigated (100 K) in the 2-methyltetrahydrofuran (2-MeTHF) matrix. This indicates that the nearest electronic excited state (triplet) is at least ∼0.3 kcal mol-1 higher in energy, that is, the triplet-quintet energy gap, ΔETQ > 0.3 kcal mol-1, which is consistent with the broken-symmetry-DFT-computed ΔETQ of about 5 kcal mol -1. In concentrated (ca. 1-10 mM) solutions of tetraradical 4 in 2-MeTHF at 133 K, a fraction of tetraradicals form a dimer (association constant, Kassoc ≈ 60 M-1), with a weak, antiferromagnetic exchange coupling, J/k ≈ -0.1 K ∼ 0.2 cal mol -1, between the S = 2 tetraradicals. This weak intradimer exchange coupling is expected for two tetraradicals at the distance of about 6 Å. The most sterically shielded tetraradical 5 in 2-MeTHF has a half-life of 1 h at room temperature; the product of its decay is the corresponding tetraamine, suggesting that the hydrogen atom abstraction from the solvent is primarily responsible for the decomposition of the tetraradical.

Original languageEnglish (US)
Pages (from-to)18205-18215
Number of pages11
JournalJournal of the American Chemical Society
Volume135
Issue number48
DOIs
StatePublished - Dec 4 2013

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Exchange coupling
Excited states
Ground state
Discrete Fourier transforms
Dimers
Energy gap
Temperature
Association reactions
Decomposition
Atoms
Hydrogen
Half-Life
Hot Temperature
Population
2-methyltetrahydrofuran

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

High-spin s = 2 ground state aminyl tetraradicals. / Rajca, Andrzej; Olankitwanit, Arnon; Wang, Ying; Boratyński, Przemysław J.; Pink, Maren; Rajca, Suchada.

In: Journal of the American Chemical Society, Vol. 135, No. 48, 04.12.2013, p. 18205-18215.

Research output: Contribution to journalArticle

Rajca, A, Olankitwanit, A, Wang, Y, Boratyński, PJ, Pink, M & Rajca, S 2013, 'High-spin s = 2 ground state aminyl tetraradicals', Journal of the American Chemical Society, vol. 135, no. 48, pp. 18205-18215. https://doi.org/10.1021/ja409472f
Rajca, Andrzej ; Olankitwanit, Arnon ; Wang, Ying ; Boratyński, Przemysław J. ; Pink, Maren ; Rajca, Suchada. / High-spin s = 2 ground state aminyl tetraradicals. In: Journal of the American Chemical Society. 2013 ; Vol. 135, No. 48. pp. 18205-18215.
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