Magnetic Interaction through Non‐Conjugated Framework Observed in Back‐to‐Back Connected Triazinyl‐Nitroxyl Biradical Derivatives
Magnetic Interaction through Non‐Conjugated Framework Observed in Back‐to‐Back Connected Triazinyl‐Nitroxyl Biradical Derivatives
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在背对背连接的三嗪基-硝酰基双自由基衍生物中观察到的通过非共轭框架的磁相互作用
DOI：
10.1002/chem.201800163
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Naoki Yoshioka
中科院分区：
文献类型：
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作者：
Yusuke Takahashi;Ryo Matsuhashi;Youhei Miura;Naoki Yoshioka
三种杂双自由基衍生物，具有背靠背连接的苯并三嗪基和共享一个共同苯并环的四甲基或四乙基异吲哚啉N-氧基的结构，3-叔丁基-1-苯基-1，4，6，8-四氢-6，6，8，8-四甲基-吡咯并[4，5-g]-1，2，4-苯并三嗪-4-基-7-氧基（1-tBu），1，3-二苯基-1，4，6，8-四氢-6，6，8，8-四甲基-吡咯并[4，5-g]-1，2，4-苯并三嗪-4-基-7-氧基（1-Ph），合成了3-叔丁基-1-苯基-1，4，6，8-四氢-6，6，8，8-四乙基-吡咯并[4，5-g]-1，2，4-苯并三嗪-4-基-7-氧基（2-tBu），并通过单晶X射线分析、变温磁化率研究和密度泛函理论计算进行了表征。1-tBu、1-Ph和2-tBu的磁化率的温度依赖性分别在70、71和43 K处表现出宽的最大值。 虽然这些自由基衍生物在固态下形成柱状或链状组装体，但聚合物基质中稀释样品的磁性测量和计算结果表明，多晶样品的磁性可以通过具有分子内反铁磁相互作用的双自旋系统来解释。磁行为可以通过使用Bleaney-Bowers模型来再现，对于1-tBu，2 J =−80.0 cm− 1，对于1-Ph，2 J =−77.1 cm− 1，对于2-tBu，2 J =−48.9 cm− 1。 中等强度的分子内反铁磁相互作用可以通过基于分子轨道理论的非共轭框架和/或通过空间相互作用的通过键相互作用来解释。N-O自旋位置与乙烯基碳原子之间的距离依赖性很强，表明轨道相互作用在分子内磁相互作用中起着重要作用。相对于1-tBu和1-Ph，2-tBu中的磁相互作用降低可以归因于四乙基的受限旋转。
Three hetero‐biradical derivatives, with the structure of a back‐to‐back connected benzotriazinyl and tetramethyl or tetraethylisoindolineN‐oxyl sharing a common benzo ring, 3‐tert‐butyl‐1‐phenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetramethyl‐pyrrolo[4,5‐g]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl (1‐tBu), 1,3‐diphenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetramethyl‐pyrrolo[4,5‐g]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl (1‐Ph), and 3‐tert‐butyl‐1‐phenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetraethyl‐pyrrolo[4,5‐g]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl (2‐tBu), were synthesized and characterized by single‐crystal X‐ray analyses, variable‐temperature magnetic susceptibility studies, and DFT calculations. Temperature dependences of the magnetic susceptibilities of1‐tBu,1‐Ph, and2‐tBuexhibit broad maxima at 70, 71, and 43 K, respectively. Although these radical derivatives form a columnar or chained assembly in the solid state, magnetic measurements of diluted samples in the polymer matrices and computational results imply that the magnetic properties of the polycrystalline sample can be explained by a two‐spin system with an intramolecular antiferromagnetic interaction. The magnetic behavior can be reproduced by using the Bleaney–Bowers model, with 2J=−80.0 cm−1for1‐tBu, 2J=−77.1 cm−1for1‐Ph, and 2J=−48.9 cm−1for2‐tBu. The moderately strong intramolecular antiferromagnetic interactions can be interpreted by a through‐bond interaction through the nonconjugated framework and/or through‐space interactions based on molecular orbital theory. The strong distance dependency between the N−O spin site and vinylic carbon atoms indicates that the orbital interaction plays an important role in the intramolecular magnetic interaction. The reduced magnetic interaction in2‐tBurelative to those of1‐tBuand1‐Phcan be attributed to restricted rotation of the tetraethyl group.