Designing Highly Axial Lanthanide Single Molecule Magnets

50多年来，经济因素推动了电子设备小型化的稳定趋势。然而，小型化的进展速度已经开始停滞，据预测，在十年内可能会达到平稳期。因此，寻求“自下而上”的替代方案来与当前的“自上而下”的方法相抗衡，以确保持续的技术进步。高密度数据存储的一个有前途的解决方案是使用单分子磁体（SMMs）。这些分子可以储存磁性信息，因此可以制造出尽可能小的设备。镧系金属（Ln） smm由于其良好的磁性而成为主要的候选材料，但目前它们只能在昂贵的液氦冷却下起作用。Ln smm保留磁性信息的温度由Ln的选择、分子几何形状和磁弛豫路径的竞争决定。这些因素都有可能得到控制，但目前人们对其放松机制仍知之甚少。松弛过程可以显著降低磁信息保留的温度，这是基于仅考虑具有明确几何形状的特定Ln所能预测的结果。因此，目标是合成具有理想金属/几何排列的Ln smm，因为这些将为磁弛豫提供最大的热障。一旦获得分子几何结构的控制和最优势垒，就可以在大温度范围内深入研究这些体系的磁弛豫路径。这种研究以前还没有在lnsmm上进行过尝试。这将使我们加深对决定弛豫机制的因素的理解，以便将来我们可以设计不支持这种过程的Ln smm，并且可以在更高的温度下存储磁信息。通过计算预测，只有两个供体原子彼此相反的镝（III） smm（两坐标，完美的轴向环境）将产生最大的热磁弛豫障碍。这些系统可以在液氮温度以上运行，在这一点上它们在技术上是可行的。Ln离子倾向于高配位数，而两坐标Ln（III）配合物目前尚不清楚，因此这将是一项了不起的合成成就。在最近的工作中，我们报道了一个六坐标Dy(III) SMM，其环境有效地模仿了我们所寻求的轴向系统，并产生了世界纪录的磁弛豫屏障（化学科学，2016,7,155）。我们对该系统设计的改进进行了理论预测，以进一步提高这一屏障，并在本提案中提出了实现这一目标的综合路线。更有野心的是，我们的目标是合成化学上可行的二坐标Dy(III) SMMs，根据我们的预测，这些SMMs可能在液氮温度以上表现出磁弛豫（无机化学，2015,54,2097）。我们最近报道了一种罕见的具有近线性几何形状的两坐标Ln（II）配合物的合成（化学通讯，2015,7,155），因此我们处于转移这些方法并制备第一个两坐标Dy(III) smm的理想位置。本提案中的所有综合研究都将辅以磁性和电子性质的高水平物理分析，包括计算建模。这将为指导我们的磁弛豫路径及其与Ln smm的几何和电子结构的关系的开创性研究提供必要的信息。理想情况下，我们可以合成可以在液氮温度下工作的Dy(III) SMM。

For over fifty years economic factors have driven a steady trend of making electronic devices smaller. However, the rate of progress in miniaturisation has started to stall, and it has been predicted that a plateau may be reached within ten years. As such, "bottom-up" alternatives are sought to rival the current "top-down" approach to ensure continued technological advancement. One promising solution for high-density data storage is to use Single Molecule Magnets (SMMs). These are molecules that can store magnetic information, and could therefore give the smallest possible devices.Lanthanide (Ln) SMMs have emerged as leading candidates due to their favourable magnetic properties, but at present these only function with expensive liquid helium cooling. The temperatures at which Ln SMMs retain magnetic information are dictated by the choice of Ln, the molecular geometry, and the competition of magnetic relaxation pathways. These factors can all potentially be controlled but at present the relaxation mechanisms are still poorly understood. Relaxation processes can significantly lower the temperature at which magnetic information is retained, based on what would be predicted solely from consideration of a specific Ln with a well-defined geometry.As such, the syntheses of Ln SMMs with ideal metal/geometry arrangements are targeted, as these will give the maximum thermal barrier to magnetic relaxation. Once control of molecular geometry and optimal barriers are obtained, the magnetic relaxation pathways of these systems can be studied in depth over a large temperature range. Such a study has not previously been attempted on Ln SMMs. This will allow us to deepen our understanding of the factors dictating relaxation mechanisms, so that in future we can design Ln SMMs that disfavour such processes and can store magnetic information at even higher temperatures.It has been predicted by calculations that dysprosium(III) SMMs with only two donor atoms set opposite to each other (a two-coordinate, perfectly axial environment) will give the largest barriers to thermal magnetic relaxation. These systems could operate above liquid nitrogen temperatures, at which point they would become technologically viable. Ln ions prefer high coordination numbers and two-coordinate Ln(III) complexes are currently unknown, hence this would be a remarkable synthetic achievement.In recent work, we have reported a six-coordinate Dy(III) SMM with an environment that effectively mimics the axial system we seek, and yielded a world-record barrier to magnetic relaxation (Chemical Science, 2016, 7, 155). We have made theoretical predictions for improvements to the design of this system to raise this barrier even further, and have set out synthetic routes to achieve this goal in this proposal. More ambitiously, we target the synthesis of chemically feasible two-coordinate Dy(III) SMMs, following our predictions that these could exhibit magnetic relaxation above liquid nitrogen temperatures (Inorganic Chemistry, 2015, 54, 2097). We have recently reported the synthesis of a rare two-coordinate Ln(II) complex with a near-linear geometry (Chemical Communications, 2015, 7, 155), hence we are in an ideal position to transfer these methodologies and prepare the first two-coordinate Dy(III) SMMs.All synthetic studies in this proposal will be complemented by high level physical analysis of magnetic and electronic properties, including computational modelling. This will provide essential information to guide our pioneering studies of magnetic relaxation pathways and their relationship to the geometry and electronic structure of Ln SMMs. Ideally we may synthesise a Dy(III) SMM that can operate at liquid nitrogen temperatures.