A Coordination Chemistry Approach to the Synthesis of Single-Molecule Magnets

本研究项目由化学部化学结构、动力学和机理B计划资助，旨在设计和研究基于过渡金属和稀土元素的新型单分子磁体。这项研究将由加州大学伯克利分校的杰弗里·R·朗教授及其同事进行。单分子磁体是一类相对较新的材料，其性能曾被认为是块状磁性材料的一部分。在极低的温度下，这些分子可以在不屈服于热随机化的情况下保持其磁化，从而使它们成为在计算机硬盘驱动器和自旋电子器件等应用中取代当前技术的有趣候选者。这项研究将在很大程度上依赖于合成化学和物理表征技术，使研究生和博士后研究员能够学习广泛的技能，为未来在学术界或行业的职业生涯做准备。重要的是，该项目还将通过参与一个旨在向年轻学生介绍各种科学主题和高等教育回报的项目，将时间用于旧金山湾区小学的外展活动。该项目还将重新设计维基百科的单分子磁体页面，以最准确和全面地反映该领域的状态，同时吸引更多对扩大他们的科学文献感兴趣的受众。该项目将寻求进一步阐明单分子磁体的结构与功能关系，以及如何最有效地调整它们的性能，以产生实际应用所需的更高的工作温度。拟议的工作分为三大类。主要目的将是更好地理解对称性和配位体磁场强度在增强磁各向异性中的作用。对于过渡金属和稀土元素，焦点将指向具有增强的磁各向异性的分子，这是由高轴对称性强制的。对于过渡金属，将以线性两坐标系为目标，而对于镧系元素，将根据每种三价金属的磁各向异性的形状选择性地选择轴向或赤道配位场。第二，磁弛豫现象将与在这些更广泛的配位场类别中所做的电子修饰相关联，以揭示对穿透势垒(隧穿)过程贡献最大的因素，最终目标是提高磁阻挡温度。这些新分子的同位素标记类似物也将被研究，以了解超精细相互作用在通过势垒松弛过程中的作用。最后一种方法是使用这种高度各向异性的单核配合物作为自由基桥联分子的构建单元，它可以显示出强耦合和大自旋基态，从而极大地减少快速松弛和随机化的可能性。

The goal of this research project, funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, is to design and study new single-molecule magnets based upon transition metal and lanthanide elements. The research will be carried out by Professor Jeffrey R. Long and coworkers at the University of California, Berkeley. Single-molecule magnets are a relatively new class of materials that exhibit properties once thought to be relegated to bulk magnetic materials. At very low temperatures, these molecules can retain their magnetization without succumbing to thermal randomization, thus rendering them intriguing candidates for replacing current technologies in applications such as computer hard drives and spintronics devices. The research will depend heavily on synthetic chemistry and physical characterization techniques, enabling graduate students and post-doctoral fellows to learn a wide array of skills in preparation for future careers in academia or industry. Importantly, the project will also devote time to outreach activities at elementary schools in the San Francisco Bay Area, through participation in a program intended to introduce young students to various topics in science and the rewards of higher education. The project will also redesign the Wikipedia Single-Molecule Magnets page to most accurately and comprehensively reflect the state of the field, while also appealing to a broader audience interested in expanding their scientific literacy.This project will seek to further elucidate the structure-function relationship in single-molecule magnets, and how their properties can be most effectively tuned to generate higher operating temperatures necessary for practical applications. The proposed work falls into three broad categories. The primary aim will be to better understand the roles of symmetry and ligand field strength in enhancing magnetic anisotropy. For both transition metals and lanthanides the focus will be directed toward molecules with enhanced magnetic anisotropy that is enforced by high axial symmetry. In the case of transition metals, linear two-coordinate systems will be targeted, while for the lanthanides, axial or equatorial ligand fields will be selectively chosen based on the shape of the magnetic anisotropy for each trivalent metal. Second, magnetic relaxation phenomenon will be correlated with electronic modifications made within these broader ligand field categories to unravel the factors that contribute most to detrimental through-barrier (tunneling) processes, with the ultimate goal of enhancing magnetic blocking temperatures. Isotopically labeled analogues of these new molecules will also be studied to understand the role of hyperfine interactions in through-barrier relaxation processes. A final approach will be to use such highly anisotropic mononuclear complexes as building units in radical-bridged molecules, which can exhibit strong coupling and large spin ground states that greatly minimize the likelihood of rapid relaxation and randomization.