手性稀土单分子磁体的合成及其多铁性能研究

A series of chiral bis-bidentate and bis-tridentate ligands with different spacers as well as chiral bidentate and tridentate ligands with different polarities will be designed and synthesized. Using these ligands along with lanthanide ions that have large magnetic anisotropy, a series of mononuclear, homo- and hetero-dinuclear chiral lanthanide single-molecule magnets will be directionally synthesized, respectively, depending on the ratio of reactants. The chiral ligands can induce the molecular structures of single-molecule magnets to be noncentrosymmetry and chirality which make them easily crystallize in polar point group that is essential for the occurrence of ferroelectricity. So, the obtained lanthanide single-molecule magnets possess not only optical activity but also possible ferroelectricity, which make them to be potential molecule-based multiferroic materials. Using these mono- and dinuclear single-molecule magnets as model systems, the comparisons and studies on the changes of slow magnetic relaxation behaviours of their single-molecule magnets and ferroelectricities will be carried out considering different factors such as the different nuclearity, coordination environment, spacer and ligands field effects resulting from the different polarities of ligands. Finally, we shall thoroughly analyse and compute the obtained results so as to probe into the rules of structure-activity relationship and the occurrence mechanisms of their multiferroic properties. Our research results not only deepen and expand the theoretic research of lanthanide single-molecule magnets but also are the theoretic foundations for the modulation of their functions and their potential application researches.

设计合成一系列具有特定配位点且配位间隔距离不等的手性双二齿和双三齿双位配体以及极性不同的手性二齿和三齿配体，通过反应物的比例调控，与具有大的磁各向异性的稀土离子定向构筑一系列单核、同和异双核手性稀土单分子磁体。由于手性配体的引入，诱导产生单分子磁体骨架结构的非中心对称和手性，使其更易结晶于极性点群从而满足具有铁电性的要求。所构筑的手性稀土单分子磁体不但具有光学活性，还可能具有铁电性，是潜在的分子基多铁材料。以定向构筑的单、双核单分子磁体为模型体系，比较和研究不同的核数、配位环境、配位间隔距离以及配体的极性变化引起的配体场效应等因素对稀土单分子磁体的慢磁弛豫行为和铁电性能的影响。对以上研究结果进行综合分析并结合理论计算，探讨材料的构效关系规律和多铁性能的产生机理。相关的研究成果不但深化和拓展了稀土单分子磁体的理论研究，而且为其功能的调控乃至潜在的应用研究奠定理论基础。

本项目设计合成了3对作为配体的手性含氮有机化合物对映体：一对双齿、一对单双齿和一对双二齿含氮有机化合物的对映体。利用合成的含氮手性配体分别与稀土或过渡金属离子配位，通过自组装反应得到了一系列稀土和过渡金属手性化合物， 其中包括单核手性稀土单离子磁体、一维链稀土单分子磁体、双核和四核分子四边形过渡金属对映体等。利用单晶X-射线衍射技术确定了它们的结构，并进行了发光、手性光学活性、磁性和铁电性能的表征和研究，详细讨论了它们的构效关系，且得到了一些有趣的研究结果。例如: 在相同的反应条件下，双齿含氮对映体与镝β-二酮中间体反应的产物分别在室温和3 ℃下结晶，得到了手性配体参与配位的镝对映体和手性配体质子化后作为平衡阳离子的镝对映体，而且手性配体参与配位的对映体具有明显加强的手性光学活性、单离子磁体和铁电性能，是潜在的分子基多铁材料。该研究结果表明，通过手性含氮配体的配位和质子化（平衡阳离子）可成功实现单核金属配合物的手性控制和物理性能的调控。该研究成果发表在国际著名的化学类综合性学术刊物Chem. Commun. (2017, 53, 3998-4001)。另外，该项目的实施结果进一步表明，金属配合物中引入手性是构筑多功能分子材料，尤其是多铁分子基材料的有效途径。