Takahashi Yusuke, Miura Youhei, Yoshioka Naoki
Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan.
Chemphyschem. 2018 Jan 19;19(2):175-179. doi: 10.1002/cphc.201701274. Epub 2017 Dec 27.
The magneto-structural correlation of hetero biradical derivatives containing a 2,2,5,5-tetramethylpyrrolin-1-yloxyl unit as a localized spin center and a verdazyl or nitronyl nitroxide radical is reported. The magnetic susceptibility measurement revealed that the verdazyl attached biradical 1 exhibits ferromagnetic interaction, whereas antiferromagnetic interaction is observed for nitronyl nitroxide attached biradical 2. An EPR study in toluene glass matrix suggests that both 1 and 2 have a ground triplet state. DFT calculations predict that there is intramolecular ferromagnetic interaction for both biradicals. The computation also suggests that the intramolecular magnetic interaction is weaker with larger dihedral angle between pyrroline ring and verdazyl ring/O-N-C-N-O plane of nitronyl nitroxide. The computations of model compounds 3 and 4 suggest that spin polarization on vinylic moiety without distribution of SOMO might be an essential condition for the intramolecular ferromagnetic interaction.
报道了含有2,2,5,5-四甲基吡咯啉-1-氧基单元作为局域自旋中心以及连氮基或硝酰基氮氧化物的杂双自由基衍生物的磁结构相关性。磁化率测量表明，连有连氮基的双自由基1表现出铁磁相互作用，而连有硝酰基氮氧化物的双自由基2则观察到反铁磁相互作用。在甲苯玻璃基质中的电子顺磁共振研究表明，1和2均具有基态三重态。密度泛函理论计算预测，两种双自由基均存在分子内铁磁相互作用。计算还表明，吡咯啉环与连氮基环/硝酰基氮氧化物的O-N-C-N-O平面之间的二面角越大，分子内磁相互作用越弱。模型化合物3和4的计算表明，乙烯基部分上没有单占据分子轨道分布的自旋极化可能是分子内铁磁相互作用的必要条件。
