Magnetic Properties of π-Conjugated Hybrid Phenoxyl-Nitroxide Radicals with Extended π-Spin Delocalization
Magnetic Properties of π-Conjugated Hybrid Phenoxyl-Nitroxide Radicals with Extended π-Spin Delocalization
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具有扩展 π 自旋离域的 π 共轭杂化苯氧基氮氧自由基的磁性
DOI：
10.1021/acs.jpca.9b11856
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Mazhukin Dmitrii
中科院分区：
文献类型：
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作者：
Zaytseva Elena;Shiomi Daisuke;Ten Yury;Gatilov Yuri V.;Lomanovich Alyona;Stass Dmitri;Bogomyakov Artem;Yu Aixia;Sugisaki Kenji;Sato Kazunobu;Takui Takeji;Bagryanskaya Elena;Mazhukin Dmitrii
合成了一系列稳定的、真正有机的开壳体系——π共轭苯氧基-硝基自由基（杂化苯氧基-硝基自由基），并研究了它们在晶体状态下的磁性能，揭示了它们作为分子磁性材料的新组成部分的应用价值。杂化苯氧基-氮氧基自由基的显著电子结构是与氮氧基部分的扩展π-自旋离域，介导了氮氧基自由基固有的局部化效应。合成了5个具有代表性的杂化自由基，其中脂肪族、芳香族和杂芳香族取代基位于致密杂化自由基中心的侧部，并通过x射线衍射分析确定了它们在结晶状态下的分子/晶体结构。杂化自由基的连续x波段ESR、1H-ENDOR光谱和DFT计算证实，未配对自旋在包括非共轭片段在内的整个分子框架上离域，这表明在晶体状态下通过取代基效应调节其电子性质的可能性。通过g张量计算分析了苯氧基部分对电子结构的显著影响。SQUID磁化测量表明，含烷基或芳香族取代基的氮氧化物表现为具有弱反铁磁（AFM） （Θ =−1 ~−2.6 K）或铁磁（FM） （Θ = +0.33 K）自旋-自旋交换作用的三维居里-魏斯顺磁体。另一方面，杂芳香取代的杂化苯氧基氮氧化物在j /kB=−25.6 K时表现出显著的AFM相互作用。基于晶体学数据和DFT计算的体磁性分析揭示了分子间AFM和FM相互作用之间的竞争，这些相互作用源于C -o （phenoxyl）···Me（nitrooxide）或(N) O-C （arom）无限1D首尾链和C(arom) -C （arom）首尾二聚体在其晶格中形成三维网络。
A series of stable and genuinely organic open-shell systems, π-conjugated phenoxyl–nitroxide free radicals (hybrid phenoxyl–nitroxide radicals), have been synthesized and their magnetic properties in the crystalline state investigated, revealing their usefulness as new building blocks for molecular magnetic materials. The salient electronic structure of the hybrid phenoxyl–nitroxide radicals is extended π-spin delocalization from the nitroxide moiety, mediating the localization effect intrinsic to nitroxide radicals. Five representative hybrid radicals containing an aliphatic, aromatic, and heteroaromatic substituent in the side part of the compact hybrid radical centers were synthesized, and their molecular/crystal structures in the crystalline state were determined by X-ray diffraction analyses. CW X-band ESR,1H-ENDOR spectroscopy, and DFT calculations for the hybrid radicals confirmed that an unpaired spin delocalizes over the whole molecular frame including the nonconjugated fragments, suggesting the possibility of tuning their electronic properties through substituent effects in the crystalline state. Significant influence of the phenoxyl moiety on the electronic structure was analyzed in terms of theg-tensor calculations. The SQUID magnetization measurements revealed that the nitroxides bearing alkyl or aromatic substituents behave as 3D Curie–Weiss paramagnets with weak antiferromagnetic (AFM) (Θ = −1 to −2.6 K) or ferromagnetic (FM) (Θ = +0.33 K) spin–spin exchange interactions. On the other hand, heteroaromatically substituted hybrid phenoxyl–nitroxide showed significant AFM interactions withJ/kB= −25.6 K. The analysis of the bulk magnetic properties based on the crystallographic data and DFT calculations revealed competition between the intermolecular AFM and FM interactions which originate from the C–O(phenoxyl)···Me(nitroxide) or (N)O–C(arom) infinite 1D head-to-tail chains and the C(arom)–C(arom) head-over-tail dimers forming 3D networks in their crystal lattices.