芳香羧酸调控的叠氮铜分子基磁性配合物的构筑及相变机理的热力学研究

本课题立意于磁学二级相变过程引起物质热力学性质的变化，选择金属铜离子作为顺磁中心、叠氮基作为连接金属离子并传递磁耦合的桥联配体，通过引入具有刚性结构的芳香羧酸作为辅助配体对其结构进行修饰，设计和合成新型配合物分子磁体，合理构建配体场和分子间作用力调控其结构和磁性。基于新型综合物性测量系统(PPMS)进行磁性配合物的低温热容测定，获得相变温度和热容的突变量，与磁性测量结果相互印证和支撑，确定热容的磁贡献最佳理论拟合模型，利用热容在分子磁体发生相变时扮演的重要且唯一的角色，探寻叠氮铜配合物分子磁体低温下磁转变与热容的关系，揭示自发磁化过程中的磁转变机理及热力学驱动内因。系统的磁性研究和热力学性质研究对设计和合成高性能配合物分子磁体及揭示二级相变过程中磁热效应的本质具有重要的理论及应用意义。

The conception of this project is that the magnetic phase transition causes the changes of thermodynamic properties. Cu(II) ions are selected as paramagnetic center, while azido groups as bridging ligand connect with metal ions and transfer of magnetic coupling, the aromatic carboxylic acids as an auxiliary ligands are introduced to the azido-Cu systems to design and prepare novel molecular magnets, employing ligand field and intermolecular interactions to tune the structure and magnetic of azido-Cu complexes. The low-temperature heat capacities of magnetic complexes are measured by the novel comprehensive physical properties measurement system (PPMS), which obtain the phase transition temperatures and the variations of heat capacity, confirming the results of magnetic measurements and determining the best theoretical fit model of magnetic contribution for heat capacity. Utilizing the important and unique role of heat capacity in the phase transition process of molecular magnets is necessary to explore the relationship between magnetic transition and low-temperature heat capacity of azide-Cu(II) molecular magnets and reveal the mechanism and thermodynamic internal cause in the process of spontaneous magnetization. Systematic study on the magnetism and thermodynamics play an important role for the design and synthesis of high-performance molecular magnets and the understanding of magnetocaloric effect in the process of second-order phase transition.