title: Structural, magnetic, and computational correlations of some imidazolo-fused 1,2,4-benzotriazinyl radicals.
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) (gsolid = 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) , gsolid = 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.
authors.affiliation: Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia (Cyprus), Fax: (+357) 22892809.
authors.forename: Christos P
authors.initials: CP
authors.lastname: Constantinides
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Berezin
authors.forename: Maria
authors.initials: M
authors.lastname: Manoli
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Leitus
authors.forename: Georgia A
authors.initials: GA
authors.lastname: Zissimou
authors.forename: Michael
authors.initials: M
authors.lastname: Bendikov
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Rawson
authors.forename: Panayiotis A
authors.initials: PA
authors.lastname: Koutentis
keywords: antiferromagnetism; exchange interactions; ferromagnetism; heterocycles; radicals