Wang Jian, Miao Hao, Xiao Zhao-Xin, Zhou Yan, Deng Lin-Dan, Zhang Yi-Quan, Wang Xin-Yi
State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center of Advanced Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China.
Dalton Trans. 2017 Aug 8;46(31):10452-10461. doi: 10.1039/c7dt01037k.
Four 2p-4f Ln-radical complexes, [(NIT-2-Pm)Ln(hfac)]·0.5CH (NIT-2-Pm = 2-pyrimidyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide, hfac = hexafluoroacetylacetonato, Ln = Tb (1), Dy (2), Ho (3) and Er (4)), and four 4f-2p-4f Ln-radical-Ln complexes, [(μ-NIT-2-Pm)Ln(hfac)(HO)]·0.5CH (Ln = Tb (5), Dy (6), Ho (7) and Er (8)) have been synthesized and characterized structurally and magnetically. These compounds can be selectively obtained by controlling the reaction ratio of Ln(hfac)·2HO to the radical ligand NIT-2-Pm. The crystal structures show that in the former four complexes 1-4, the NIT-2-Pm radical acts as a terminal bidentate ligand chelating to one Ln ion, while in 5-8, the NIT-2-Pm acts as a bridging ligand linking two Ln ions to form a binuclear three-spin system. Magnetic studies revealed that complexes 1-4 and 6 show frequency-dependent ac magnetic susceptibilities, suggesting a possible single-molecule magnet behavior. To the best of our knowledge, complexes 3 and 4 are the first Ho-NIT and Er-NIT compounds showing slow magnetic relaxation. Compounds 5-8 represent a rare family of compounds showing the NIT bridged 4f-2p-4f three-spin motif, while complex 6 is a rare NIT bridged multinuclear lanthanide compound possessing SMM-like behaviour. Ab initio calculations were performed on all these complexes. The fitting of the magnetic susceptibilities of these compounds suggests weak antiferromagnetic coupling between the Ln and NIT radical in 1-8 and weak ferromagnetic Ln-Ln interactions in 5-8.
合成并通过结构和磁性表征了四种2p-4f镧系元素自由基配合物，[(NIT-2-Pm)Ln(hfac)]·0.5CH（NIT-2-Pm = 2-嘧啶基-4,4,5,5-四甲基-4,5-二氢-1H-咪唑-1-氧基-3-氧化物，hfac = 六氟乙酰丙酮，Ln = Tb (1)、Dy (2)、Ho (3) 和 Er (4)），以及四种4f-2p-4f镧系元素-自由基-Ln配合物，[(μ-NIT-2-Pm)Ln(hfac)(HO)]·0.5CH（Ln = Tb (5)、Dy (6)、Ho (7) 和 Er (8)）。通过控制Ln(hfac)·2HO与自由基配体NIT-2-Pm的反应比例可以选择性地得到这些化合物。晶体结构表明，在前四种配合物1-4中，NIT-2-Pm自由基作为末端双齿配体与一个Ln离子螯合，而在5-8中，NIT-2-Pm作为桥联配体连接两个Ln离子形成双核三自旋体系。磁性研究表明，配合物1-4和6表现出频率依赖性交流磁化率，表明可能存在单分子磁体行为。据我们所知，配合物3和4是首例表现出缓慢磁弛豫的Ho-NIT和Er-NIT化合物。化合物5-8代表了一类罕见的显示NIT桥联4f-2p-4f三自旋 motif的化合物，而配合物6是一种罕见的具有类单分子磁体行为的NIT桥联多核镧系化合物。对所有这些配合物进行了从头算计算。这些化合物磁化率的拟合表明，在1-8中Ln与NIT自由基之间存在弱反铁磁耦合，在5-8中存在弱铁磁Ln-Ln相互作用。
