Magnetic interactions in p-phenylene-bis(nitronyl nitroxide) biradicals with large torsion angles
Magnetic interactions in p-phenylene-bis(nitronyl nitroxide) biradicals with large torsion angles
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DOI：
10.1016/j.poly.2006.09.034
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发表时间：
2007-06
期刊：
影响因子：
2.6
通讯作者：
Y. Kanzaki;D. Shiomi;T. Ise;Kazunobu Sato;T. Takui
中科院分区：
文献类型：
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作者：
Y. Kanzaki;D. Shiomi;T. Ise;Kazunobu Sato;T. Takui
我们设计并合成了在2,3-(2)和2,5-(3)位置上被两个甲氧基取代的对苯双（硝基硝基）双自由基。母体双基对苯-双硝基氮氧化物(1)分子内反铁磁交换作用为2J/kB=−104K ~−106K，硝基氮氧化物的苯基环和咪唑环之间的扭转角为28.5°。x射线晶体结构分析表明，2和3中体积较大的取代基产生了65-70°的大扭转角。较大的扭转角会减弱分子内交换作用的强度，这是由于对苯基和自由基之间的π共轭作用减小所致。磁化率测量表明，2和3的分子内交换相互作用严重减弱，约为1,2 j /kB= - 6K ~ - 8K的6%。扭转角与分子内交换相互作用之间的关系与DFT计算结果一致。具有抑制分子内交换相互作用的基态单重态双基可以作为理论研究中预测的外来交换耦合自旋系统的基石。
We have designed and synthesized new biradicals of p-phenylene-bis(nitronyl nitroxide) substituted with two methoxy groups at 2,3- (2) and 2,5-positions (3). A parent biradical p-phenylene-bis(nitronyl nitroxide) (1) has intramolecular antiferromagnetic exchange interaction of 2J/kB=−104K∼−106K with a torsion angle of 28.5° between the phenyl and the imidazole rings of nitronyl nitroxide. X-ray crystal structure analysis shows that the bulky substituents in 2 and 3 give large torsion angles of 65–70°. The larger torsion angles should weaken the magnitude of intramolecular exchange interactions, which is attributed to a decrease in π-conjugation over the p-phenylene and the radical groups. Magnetic susceptibility measurements indicate that the intramolecular exchange interactions in 2 and 3 are severely weakened to about 6% of that in 1, 2J/kB=−6K∼−8K. The relation between the torsion angle and the intramolecular exchange interaction is consistent with DFT calculations. The ground-state singlet biradicals with suppressed intramolecular exchange interactions can be a building block for exotic exchange-coupled spin systems as predicted in our theoretical studies.