两类新型稀土金属有机单离子磁体的设计、合成与调控

Single-ion magnets (SIMs) are a specific type of molecules which contain only single paramagnetic center and can exhibit the fascinating magnetic relaxation phenomena at the single-molecular level. Recently, organolanthanide SIMs have been a hot research area not only because it is an interdisciplinary field of organolanthanide chemistry and the molecular magnetism, but also because this type of SIMs usually own superior magnetic properties. From these points, we will design and synthesize two novel types of organolanthanide SIMs, and tune the negative charge distribution of the coordination sphere by ligand modifications in order to maximize the magnetic anisotropy, thereby achieving organolanthanide SIMs with superior magnetic behavior. Specifically it includes: (1) Modify the ligand on the mononuclear arene-organolanthanide complexes to explore the mechanism of the influence of the neutral arene on the magnetic anisotropy and the enhancement of magnetic properties by structural modifications. (2) Design and synthesize a six-coordinated Ln-SIM, and study the enhancement of magnetic properties by means of structural diversity, which will be helpful to the investigation of the magneto-structural relationship. (3) To gain an insight into the relationship between the magnetic anisotropy and the negative charge distribution caused by ligand modifications, we will investigate the magnetic easy axis, the low-lying energy levels distribution and the magnetic relaxation mechanism by using quantum chemistry method (ab initio method) and electrostatic analysis.

单离子磁体是一类在单分子水平上表现出磁弛豫行为且只含有一个顺磁金属离子的分子。近几年，稀土金属有机单离子磁体已经成为研究热点，它不仅将稀土金属有机化学与分子磁性领域有效地结合起来，而且该类单离子磁体通常表现出较优的磁学性能。本项目将设计合成两类新型稀土金属有机单离子磁体，并修饰配体来调控配位环境中负电荷的分布，以期实现磁各向异性的最大化，进而得到性能更优异的单离子磁体。具体研究内容包括：(1)微调中性芳环稀土金属有机配合物的结构，探究中性芳环配体对磁各向异性的影响机理以及结构微调对磁性进行改善；(2)设计并合成目前比较少见的六配位稀土单离子磁体，利用有机配体的多样性来提升单离子磁体性能并研究磁构关系；(3)理论研究将利用量子化学从头算方法和静电势分析等来进一步深入探讨结构微调引起的负电荷分布变化与磁各向异性的关系，确定单离子磁体的磁各向异性轴以及微观电子能级分布情况，并研究磁弛豫机理等。

单离子磁体是一类在单分子水平上表现出磁弛豫行为且只含有一个顺磁金属离子的分子。本项目合成并研究了多例新型单离子磁体：（1）在中性芳环稀土单离子磁体体系中，对镝配合物的结构进行了一系列微调，实验结果表明该类分子结构的局域对称性越接近D5h，相应的磁学性能越好；同时，中性芳环配体较其它配体对磁性的影响更明显。（2）在六配位稀土单离子磁体中，镝配合物为首例可在零场下表现出单离子磁体行为的三棱柱型稀土单离子磁体；对其多磁弛豫过程的贡献情况分析表明，高温区占主导的为Raman过程，而不是Orbach过程；结合理论计算及负电荷分布分析，提出了进一步提升该类配合物磁各向异性的策略。（3）基于席夫碱配体HL构筑了一系列单核稀土配合物，并系统地研究了末端取代基对结构组成及磁各向异性的影响，研究发现配合物中参与配位的HL配体数目与末端取代基的供吸电子能力强弱相关，且由强吸电子取代基构筑的配合物具有更优异的单离子磁体行为。以上工作对进一步设计合成单离子磁体、提升磁各向异性、深入理解磁弛豫过程等具有指导意义。