Low-Coordinate and Radical-Bridged Lanthanide Molecular Nanomagnets

从简单的化学构件合成复杂的磁性材料，封装了分子磁性的内在魅力。分子磁体通常是使用自下而上的方法设计的，这种方法提供了进入理论模型(如配位场理论)的实验试验台。分子方法还使合理的应用方法成为可能，例如使用过渡金属络合物作为量子计算的量子比特，使用稀土络合物作为磁性制冷剂，以及在核磁共振光谱中作为位移试剂和磁共振成像。目前值得考虑的工作集中在分子系统中的磁双稳现象，即在相同的物理条件下可以测量两种不同的磁响应。自旋交叉(SCO)化合物和单分子磁体(SMM)是两种重要的双稳分子磁体。基于3D金属(主要是FeII)的SCO材料的双稳态使这些材料被提议用于显示器、传感器和信息存储设备。同样，SMM是由磁化反转的有效能垒定义的d-和f-块配位化合物，也因其磁双稳而被用于信息存储设备。尽管SCO化合物和SMM具有双稳特性，但这两种现象在不同的温度范围内观察到；SCO倾向于发生在50-350K区域，而SMM行为通常发生在50K以下，如果能够获得这两种现象的系统，它们将提供一条双功能分子磁体的途径，其中SCO和SMM现象以一种协同的方式相互影响。这一雄心面临的第一个挑战是，获得SCO-SMM材料的一般合成路线极其罕见：在这个项目中，将开发由镧系元素SMM和SCO化合物组成的超分子结构，以使用新的合成方法来探索双功能分子磁体的性能。第二个挑战将是了解上海合作组织和SMM现象如何通过磁交换等因素相互影响。为了实现这一点，我们将在分子和超分子(轮烷)尺度上研究SCO-SMM，从而允许通过键和通过空间的相互作用被探测、理解和控制。将实现以下里程碑：里程碑1：一种用于合成具有相互依赖的SCO和SMM性质的异双金属Fe-Ln配合物的通用方法-基于掩蔽的二价稀土试剂的反应性。里程碑2：合成独特的轮烷分子磁体家族-包括光激活的衍生物-其中SCO和SMM亚基之间的通信是通过客体分子介导的。里程碑3：基于一系列物理技术对SCO-SMM的详细表征。里程碑4：对SCO-SMMS的理论理解，并能够利用这种理解通过受控的合成修饰来增强磁性。

The synthesis of complex magnetic materials from simple chemical building blocks encapsulates the intrinsic fascination of molecular magnetism. Molecular magnets are typically designed using bottom-up approaches that provide access to experimental testbeds for theoretical models such as ligand field theory. The molecular approach also enables rational approaches to applications, such as the use of transition metal complexes as qubits for quantum computing, the use of lanthanide complexes as magnetic refrigerants, and in NMR spectroscopy as shift reagents and in magnetic resonance imaging.Considerable effort is currently focused on the phenomenon of magnetic bistability in molecular systems, whereby two different magnetic responses can be measured under identical physical conditions. Two important types of bistable molecular magnets are spin-crossover (SCO) compounds and single-molecule magnets (SMMs). The bistability of SCO materials based on 3d metals (predominantly FeII) has allowed these materials to be proposed for applications in displays, sensors and information storage devices. Similarly, SMMs, which are d- and f-block coordination compounds defined by an effective energy barrier to reversal of their magnetization, have also been suggested for use in information storage devices by virtue of their magnetic bistability.Despite the bistability in SCO compounds and in SMMs, the two phenomena are observed in different temperature regimes; SCO tends to occur in the 50-350 K regime, whereas SMM behaviour usually occurs below 50 K. If systems displaying both phenomena could be obtained, they would provide a route to bifunctional molecular magnets in which the SCO and SMM phenomena influence each other in a synergic way. The first challenge confronting this ambition is that general synthetic routes to SCO-SMM materials are extremely rare: in this project supramolecular architectures consisting of lanthanide SMMs and SCO compounds will be developed in to explore the properties of bifunctional molecular magnets using a novel synthetic methodology. The second challenge will be to understand how the SCO and SMM phenomena influence each other via factors such as magnetic exchange. To achieve this, we will study SCO-SMMs on the molecular and supramolecular (rotaxane) scales, thus allowing through-bond and through-space interactions to be probed, understood and controlled. The following milestones will be achieved:Milestone 1: a general method - based on the reactivity of 'masked' divalent lanthanide reagents - for the synthesis of heterobimetallic Fe-Ln complexes with interdependent SCO and SMM properties.Milestone 2: synthetic route to a unique family of rotaxane molecular magnets - including photoactivated derivatives - in which communication between SCO and SMM subunits is mediated via the guest molecule.Milestone 3: detailed characterization of SCO-SMMs based on a range of physical techniques.Milestone 4: Theoretical understanding of the SCO-SMMs, with an ability to use this understanding to enhance the magnetic properties through controlled synthetic modifications.