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 language | English |
|---|---|
| Pages (from-to) | 5388-5396 |
| Number of pages | 9 |
| Journal | Chemistry - A European Journal |
| Volume | 20 |
| Issue number | 18 |
| DOIs | |
| Publication status | Published - Apr 25 2014 |
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Keywords
- antiferromagnetism
- exchange interactions
- ferromagnetism
- heterocycles
- radicals
ASJC Scopus subject areas
- Chemistry(all)
Cite this
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 journal › Article
}
TY - JOUR
T1 - Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals
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.
AU - Koutentis, Panayiotis A.
PY - 2014/4/25
Y1 - 2014/4/25
N2 - 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).
AB - 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).
KW - antiferromagnetism
KW - exchange interactions
KW - ferromagnetism
KW - heterocycles
KW - radicals
UR - http://www.scopus.com/inward/record.url?scp=84899636406&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84899636406&partnerID=8YFLogxK
U2 - 10.1002/chem.201304538
DO - 10.1002/chem.201304538
M3 - Article
AN - SCOPUS:84899636406
VL - 20
SP - 5388
EP - 5396
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 18
ER -