Characterization and Magnetic Properties of a "Super Stable" Radical 1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl
Characterization and Magnetic Properties of a "Super Stable" Radical 1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl
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DOI：
10.1021/jo200210s
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发表时间：
2011-04-15
影响因子：
3.6
通讯作者：
Tasiopoulos, Anastasios J.
中科院分区：
文献类型：
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作者：
Constantinides, Christos P.;Koutentis, Panayiotis A.;Tasiopoulos, Anastasios J.
1,3-二苯基-7-三氟甲基-1,4-二氢-1,2,4-苯并三嗪-4-基 (4)，通过使用 Pd/C (1.6 mol %) 和 1,8-二氮杂双环[5.4.0]十一碳-7-烯 (0.1 当量) 在空气中催化氧化相应的氨基腙 5，以高收率制备，在空气中稳定。 MnO2 和 KMnO4 存在下的二氯甲烷溶液。此外，自由基 4 在远高于其熔点（160-161 摄氏度）时具有热稳定性，分解起始温度为 288 摄氏度。X 射线研究表明，自由基 4 沿 a 轴以等距滑动的 pi 堆叠形式堆积。循环伏安法显示两个完全可逆的波，对应于-1/0、0/+1过程。 EPR研究表明自旋密度主要离域在杂环的三嗪基片段上。 5-300 K 区域的磁化率测量表明，自由基在低至 10 K 时遵循居里韦斯行为（C = 0.376 emu .K. mol(-1) 和 0 = +1.41 K），与 S = 1/2 自由基之间的弱铁磁相互作用一致。随后将磁性数据拟合到一维铁磁链模型，在低至 10 K 时提供了良好的拟合（g = 2.00，J/k = +1.49K），但未能重现较低温度下 T-X 的后续下降，这归因于铁磁链之间反铁磁相互作用开始减弱。
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 degrees C) with a decomposition onset temperature of 288 degrees C. X-ray studies show that radical 4 packs in equidistant slipped pi-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 0 = +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 = +1.49K) down to 10 K but failed to reproduce the subsequent decrease in T-X at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains.