基于稀土高核簇合物的分子磁性材料研究

Presently, there is only a little study about the single-molecule magnets of high-nuclearity lanthanide clusters, and the scientific problem about their magnetic mechanism and the relationship of the magnetism and structure remains to be solved. On the other hand, there may exist simultaneously multiple metal centers with different coordination number and coordination environment, and multiple units with different structure in high-nuclearity lanthanide clusters, which is helpful for the study of magnetic mechanism of lanthanide-based single-molecule magnets. Due to their large molecular size, the study on the magnetic properties of the high-nuclearity lanthanide clusters can become the bridge between classical and quantum magnetic theory. These characteristics make the study on the high-nuclearity lanthanide clusters very meaningful. This project intends to study the synthesis and magnetic properties of lanthanide clusters with more than ten nuclearities or even over twenty nuclearities by the design and synthesis of series of di-acylhydrazone ligands with multiple bridging groups. The influence of the ligand structure, the auxiliary ligands, the anions, the assembly methods and conditions on the composition and structure of the clusters will be studied, and the effect of the coordination environment, coordination geometry, and coordination symmetry of the lanthanide ion, the substituents of the ligand, the structural units of the clusters on the magnetic properties will be investigated. These studies will provide theoretical and experimental evidence for the magnetic mechanism, the relationship of magnetism and structure, and the regulation of magnetic property of the high-nuclearity lanthanide clusters. The research of the project will deepen the understanding of the magnetic mechanism of lanthanide molecule-based magnetic materials, and find new lanthanide molecule materials with excellent magnetic performance, and thus is of great theoretical and practical significance.

目前，稀土高核簇合物单分子磁体研究还很少，其磁性机制及磁构效关系是一个有待解决的科学问题。另一方面，稀土高核簇合物可能同时存在多个不同配位数和配位环境的金属中心及不同的结构单元，有助于稀土单分子磁体磁性机制研究；其大的分子尺寸使其磁性质研究可成为磁学经典和量子理论研究之间的桥梁，对其开展研究很有意义。本项目拟通过设计合成系列含多桥联基团的双酰腙配体，合成十核甚至二十核以上的稀土高核簇合物，研究簇合物的磁性质。项目将研究配体结构、辅助配体、阴离子、组装方法及条件等因素对稀土高核簇合物组成及结构的影响；研究稀土离子配位环境、配位几何构型、配位对称性以及配体取代基、簇合物结构单元及连接方式等因素对磁性质的影响，为解决稀土高核簇合物的磁性机制、磁构效关系及磁性能调控问题提供理论和实验依据。项目研究将会深化对稀土基分子磁性材料磁性机制的了解，发现性能优良的稀土分子磁性材料，具有理论和实际意义。

基于稀土高核簇的分子基磁性材料，因其自旋堆砌方式与磁传递途径的新颖性与多样性，及其纳米化的尺寸，有望表现低核体系所不具备的特殊磁性，且其可作为经典和量子理论研究之间的桥梁，因而引起人们的研究兴趣。但其合成难度大，现存体系也很有限。故而此类分子的研究是兼具重要意义与挑战性的前沿课题之一。根据特定的配体设计思想，本项目合成了母体桥连或配位元素能与两翼酰腙基团产生协同配位的双酰腙配体、以及具备类似结构特征以实施比较研究的双羧酸、单酰腙及席夫碱配体。通过母体与端基的骨架、桥连元素、取代基位阻的变化合成了系统多样的多齿配体。在辅助配体、阴离子、脱质子碱、组装方法及条件等因素的调控下，项目以设计合成的配体组装了102例新型配合物，成功构建了稀土高核簇分子库。所得簇的结构兼具多样性与系统性，且普遍呈现较高的核数、新颖的拓扑与大的纳米尺寸，代表性的如{Dy30}笼、由2对{Dy30}组成的双笼状{Dy60}、{Dy20}笼、环状{Ln24}、单股{Gd18}轮、{Ln16}双轮、漏斗状{Ln12}及双船式{Ln11}等。基于配体及组装条件的变化，项目系统探讨了各合成因素对稀土簇的组装及其结构的影响，重点结合高分辨质谱深入研究了部分体系的组装过程，由此提炼了此类簇的组装规律。合成的多数Dy簇与Gd簇分别表现出优良的单分子磁体性能与磁致冷效应，如呈现双重弛豫等特殊磁行为的{Dy10}，以及最大磁熵变值分别为36.35、30.05、30.25 J kg−1 K−1的{Gd18}、{Gd11}与{Gd24}等。基于配体与所得簇系统性的结构变化，项目研究了配体结构、稀土离子的种类与配位几何构型、桥连因素及自旋堆砌方式等因素对簇磁性能的影响，总结了此类簇的磁性机制与磁效关系。项目在配体设计、合成方法、组装过程及簇的结构特征等方面均凸显研究特色。项目研究为稀土高核簇基磁性材料的有效组装与性能调控提供了理论和实验依据，对深化和拓展稀土基分子磁性材料的设计合成与应用研究具有重要意义。