磁交换扰动下高能垒单分子磁体的有序组装及零场隧穿研究

As the high energy barriers achieved in rare-earth single-ion magnets and nice hysteresis loops obtained in low-nuclearity rare-earth single-molecule magnets, we aim to combine the high energy barriers and magnetic exchange interactions to synthesize high-temperature single-molecule magnets, and to study the effect of exchange interactions on the blocking temperature and magnetic relaxation process deeply. In the case of DyIII ion, of which the basic overall shape of free-ion electron density is oblate, constructing a coordination environment with one or two strong ligand coordinating to the central DyIII ion along the axial direction can easily produce a large magnetic anisotropy (high energy barrier), and can keep the easy axis along the direction of DyIII ion to strong-field coordination. And then, introducing magnetic exchange interaction whether via axial direction by head-to-head or via equatorial direction by shoulder-to-shoulder manner, not only can preserve the large magnetic anisotropy, but also align the paramagnetic ions parallel to each other. Four ways including i) diamagnetic atom/group ii) radical iii) 3d metal ion iv) metal−metal bond are considered to introduce intramolecular exchange interactions. In addition to creating a more classical coupled system with large total angular momentum, magnetic coupling can suppress quantum tunneling of the magnetization at zero field, forcing thermally activated relaxation behavior over a much broader temperature range, and thus giving a higher blocking-temperature single-molecule magnets. Further experimental technique and theoretical calculation are used to evaluate the effect of magnetic exchange interactions on the relaxation processes such as quantum tunneling process, finding the relationship between the magnetism and structure and advancing the development of single-molecule magnets.

针对稀土单离子磁体较高的能垒和稀土低核单分子磁体较好的磁滞回线的现状，本项目旨在把高能垒和磁交换作用结合起来，合成高温单分子磁体，深入研究磁交换对单分子磁体阻塞温度和磁弛豫过程的影响。以基态电子云密度为扁平型的DyIII离子为例，在轴向构建一个或者两个强场配体配位，使其易形成强的轴向磁各项异性(高的能垒值)，且把易磁化轴方向控制在稀土离子和强场配位方向。然后通过头碰头或者肩并肩的方式在轴向上或者平面上引入磁交换作用，这样既能保留稀土离子强磁各项异性，又能使顺磁离子的各向异性轴尽量平行排列。拟通过i)抗磁原子/基团ii)自由基iii)3d金属iv)金属金属键桥连引入分子内磁交换作用，在增大总角动量的同时抑制零场量子隧穿过程，延长热激发弛豫温度范围，获得高阻塞温度单分子磁体，进而分析磁–构关系，利用实验手段和理论计算分析磁交换作用与零场量子隧穿等磁弛豫过程之间的关联，推进单分子磁体性能的优化。

单分子磁体是一类具有磁双稳态的磁性分子，能在分子尺度上进行信息处理与存储，在高密度信息存储和量子信息处理领域有着诱人的应用前景。目前，单分子磁体典型的磁体行为仍在数十K，可操作温度较低，严重制约了其应用前景。鉴于稀土单离子磁体较高的能垒和稀土低核单分子磁体较好的磁滞回线，该项目旨在把高能垒和磁交换作用结合起来，合成高温单分子磁体，深入研究磁各向异性和磁交换作用对单分子磁体阻塞温度和磁弛豫过程的影响，推进单分子磁体性能的优化。. 项目从稀土单离子磁体出发，从轴向配体场、平面配体场、局域对称性、金属离子等方面开展了磁各向异性的调控研究，包括通过弱化平面配体的配位能力提升单分子磁体性能；通过氢键稳固的方法引入端基氟离子配位合成镝基单分子磁体；结合C5轴对称性和轴向强场配体构筑系列五角双锥高性能单分子磁体；合成创新纪录的五角双锥构型钬基单分子磁体。在此研究基础上，结合强磁各向异性，引入常规桥联配体，以稀土双核簇为主，从磁各向异性和磁交换作用两方面开展稀土单分子磁体的磁弛豫动力学研究，主要包括：利用大位阻胺类配体合成氯桥连双核镝单分子磁体，其能垒突破当时所报道氯桥连镧系单分子磁体的极限，并发现磁交换作用可能会引起独立的磁弛豫过程；改进配体，利用双酚螯合配体合成另一例高能垒的氯桥连双核镝单分子磁体，发现分子内磁交换作用可以起到磁偏置效应从而有效抑制零场量子隧穿。进一步把桥联基团从抗磁基团拓展至具有弥散价电子轨道的自由基，通过独特的氧化氢醌的方法合成第一例具有结构表征的1,4-半醌自由基桥连稀土配合物，并获得首例1,4-半醌自由基稀土单分子磁体。. 总体而言，该项目开发了若干高性能单分子磁体，并通过磁各向异性的调控以及磁交换作用的扰动来优化单分子磁体性能，推进单分子磁体的发展。在此项目的资助下，以第一作者或者通讯作者发表论文8篇，包括Chem. Commun., Chem. Eur. J., Inorg. Chem.等。