Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals

Christos P. Constantinides, Andrey A. Berezin, Maria Manoli, Gregory M. Leitus, Georgia A. Zissimou, Michael Bendikov, Jeremy M. Rawson, Panayiotis A. Koutentis

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

1,3,7,8-Tetraphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (5), 8-(4-bromophenyl)-1,3,7-triphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4] benzotriazin-4-yl (6), and 8-(4-methoxyphenyl)-1,3,7-triphenyl-4,8-dihydro-1H- imidazolo[4,5g][1,2,4]benzotriazin-4-yl (7) were characterized by using X-ray diffraction crystallography, variable-temperature magnetic susceptibility studies, and DFT calculations. Radicals 5-7 pack in 1 D π stacks made of radical pairs with alternate short and long interplanar distances. The magnetic susceptibility (χ vs. T) of radicals 5 and 6 exhibit broad maxima at (50±2) and (50±4) K, respectively, and are interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with average exchange-interaction values of J=-31.3 and -35.4 cm-1 (g solid=2.0030 and 2.0028) and an alternation parameter a=0.15 and 0.38 for 5 and 6, respectively. However, radical 7 forms 1 D columns of radical pairs with alternating distances; one of the interplanar distances is significantly longer than the other, which decreases the magnetic dimensionality and leads to discrete dimers with a ferromagnetic exchange interaction between the radicals (2J=23.6 cm-1, 2zJ′=-2.8 cm-1, g solid=2.0028). Magnetic exchange-coupling interactions in 1,2,4-benzotriazinyl radicals are sensitive to the degree of slippage and inter-radical separation, and such subtle changes in structure alter the fine balance between ferro- and antiferromagnetic interactions. Bigger is stronger: π-Extension of 1,2,4-benzotriazin-4-yl radicals leads to an enhanced overlap between SOMO orbitals and, therefore, to a strong effective exchange coupling within alternating 1 D chains of imidazolo-benzotriazinyls. However, subtle changes in interplanar distances and slippage angles switch the observed magnetic properties (see figure).

Original languageEnglish
Pages (from-to)5388-5396
Number of pages9
JournalChemistry - A European Journal
Volume20
Issue number18
DOIs
Publication statusPublished - Apr 25 2014

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Exchange coupling
Exchange interactions
Magnetic susceptibility
Crystallography
Discrete Fourier transforms
Dimers
Magnetic properties
Switches
X ray diffraction
Temperature

Keywords

  • antiferromagnetism
  • exchange interactions
  • ferromagnetism
  • heterocycles
  • radicals

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Constantinides, C. P., Berezin, A. A., Manoli, M., Leitus, G. M., Zissimou, G. A., Bendikov, M., ... Koutentis, P. A. (2014). Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals. Chemistry - A European Journal, 20(18), 5388-5396. https://doi.org/10.1002/chem.201304538

Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals. / Constantinides, Christos P.; Berezin, Andrey A.; Manoli, Maria; Leitus, Gregory M.; Zissimou, Georgia A.; Bendikov, Michael; Rawson, Jeremy M.; Koutentis, Panayiotis A.

In: Chemistry - A European Journal, Vol. 20, No. 18, 25.04.2014, p. 5388-5396.

Research output: Contribution to journalArticle

Constantinides, CP, Berezin, AA, Manoli, M, Leitus, GM, Zissimou, GA, Bendikov, M, Rawson, JM & Koutentis, PA 2014, 'Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals', Chemistry - A European Journal, vol. 20, no. 18, pp. 5388-5396. https://doi.org/10.1002/chem.201304538
Constantinides, Christos P. ; Berezin, Andrey A. ; Manoli, Maria ; Leitus, Gregory M. ; Zissimou, Georgia A. ; Bendikov, Michael ; Rawson, Jeremy M. ; Koutentis, Panayiotis A. / Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals. In: Chemistry - A European Journal. 2014 ; Vol. 20, No. 18. pp. 5388-5396.
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AU - Constantinides, Christos P.

AU - Berezin, Andrey A.

AU - Manoli, Maria

AU - Leitus, Gregory M.

AU - Zissimou, Georgia A.

AU - Bendikov, Michael

AU - Rawson, Jeremy M.

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KW - antiferromagnetism

KW - exchange interactions

KW - ferromagnetism

KW - heterocycles

KW - radicals

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