Characterization and Magnetic Properties of a “Super Stable” Radical 1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl

• Published in: Journal of organic chemistry Vol. 76; no. 8; pp. 2798 - 2806
• Main Authors: Constantinides, Christos P, Koutentis, Panayiotis A, Krassos, Harry, Rawson, Jeremy M, Tasiopoulos, Anastasios J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.04.2011
• Subjects: Chemistry; Exact sciences and technology; Free radicals chemistry; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties; Reactivity and mechanisms; Nitrogen heterocycle; EPR spectrometry; Ferromagnetic materials; Molecular interaction; Spin density; Decomposition; Magnetic susceptibility; Characterization; Cyclic voltammetry; Oxidation; Chemical synthesis; Magnetic properties; 1,8-Diazabicyclo[5.4.0]undec-7-ene; Benzotriazine derivatives; Chemical solution; Catalytic reaction; Antiferromagnetic materials; Electron delocalization; Air; X ray diffraction; Amidrazone; Potassium Permanganates; Manganese IV Oxides; Pi-System; Organic free radical; Triazine derivatives; Dichloromethane; Manganese Oxides; Fluorine Organic compounds; Melting point
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo200210s

1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (4), prepared in high yield via the catalytic oxidation of the corresponding amidrazone 5 by using Pd/C (1.6 mol %) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1 equiv) in air, is stable in dichloromethane solutions in the presence of MnO2 and KMnO4. Furthermore, radical 4 is thermally stable well past its melting point (160−161 °C) with a decomposition onset temperature of 288 °C. X-ray studies show that radical 4 packs in equidistant slipped π-stacks along the a axis. Cyclic voltammetry shows two fully reversible waves, corresponding to the −1/0, 0/+1 processes. EPR studies indicate that the spin density is mainly delocalized on the triazinyl fragment of the heterocycle. Magnetic susceptibility measurements in the 5−300 K region showed that the radical obeys Curie−Weiss behavior down to 10 K (C = 0.376 emu·K·mol−1 and θ = +1.41 K) consistent with weak ferromagnetic interactions between S = 1/2 radicals. Subsequent fitting of the magnetic data to a 1D ferromagnetic chain model provided an excellent fit (g = 2.00, J/k = +1.49 K) down to 10 K but failed to reproduce the subsequent decrease in χT at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains.