Premium
Structural, Magnetic, and Computational Correlations of Some Imidazolo‐Fused 1,2,4‐Benzotriazinyl Radicals
Author(s) -
Constantinides Christos P.,
Berezin Andrey A.,
Manoli Maria,
Leitus Gregory M.,
Zissimou Georgia A.,
Bendikov Michael,
Rawson Jeremy M.,
Koutentis Panayiotis A.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304538
Subject(s) - radical , antiferromagnetism , chemistry , crystallography , magnetic susceptibility , ferromagnetism , condensed matter physics , physics , organic chemistry
1,3,7,8‐Tetraphenyl‐4,8‐dihydro‐1 H ‐imidazolo[4,5 g ][1,2,4]benzotriazin‐4‐yl ( 5 ), 8‐(4‐bromophenyl)‐1,3,7‐triphenyl‐4,8‐dihydro‐1 H ‐imidazolo[4,5 g ][1,2,4]benzotriazin‐4‐yl ( 6 ), and 8‐(4‐methoxyphenyl)‐1,3,7‐triphenyl‐4,8‐dihydro‐1 H ‐imidazolo[4,5 g ][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 (2 J =23.6 cm −1 , 2 zJ ′=−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.