基于两性离子型配体的类卤素-膦酸根(-羧基)混桥单链磁体的设计与性质研究

Single-chain magnet (SCM) is important for scientific research and in the frontiers of molecular magnetism. The research of SCM is significant for basic theory and practical application. One of the key issues for SCM design is the control of interchain magnetic exchange. In this project, according to the rule of coordination chemistry, a kind of zwitterionic ligands with different shape and length will be chosen or designed, which has phosphonate-carboxylate groups and contains positive molecular skeleton and saturated hydrocarbon groups. These ligands will be used for linking the mix-bridged (pseudohalogen-phosphonate(-carboxylate) bridges) chains into high-dimensional frameworks as to weaken the interchain magnetic exchange. It is helpful to get the systems which have magnetic isolated chains with interchain covalent linkage and further the design and the modulation of SCM can be realized. We will further study how to tune structures and magnetic behaviors by adsorption/desorption guest molecules. This project will provide research foundation, academic value and application prospect from magnetic complexes to multifunctional molecular materials. These materials has promising applications such as magnetic sensors, magnetic switchers, magnetic separation media and so on.

单链磁体是分子磁学领域里具有重要科学研究意义的前沿课题，对其磁性的研究无论在基础理论方面还是在实际应用方面都有非常重大的意义。单链磁体设计的关键问题之一是链间磁相互作用的控制。本项目根据配位化学原理，选择和设计不同形状和长度的含正电性骨架和饱和碳氢基团的两性离子型膦酸-羧基桥联配体，将类卤素-膦酸根(-羧基)混桥链连接成高维结构并降低链间磁相互作用，获得结构上链间共价连接但磁性上链间隔离的体系，进而实现单链磁体的设计和磁性调控；在此基础上进一步研究具有溶剂分子的磁性配位聚合物在客体吸脱附过程中骨架发生的变化，进而导致的磁性变化。这为从单一磁性质的分子材料向具有复合功能的分子材料的研究奠定基础，具有一定学术价值和应用前景。这种客体分子调控的磁性材料在磁性传感、磁性开关、磁性分离等方面有潜在的应用价值。

分子磁性材料是由磁性金属离子和短桥配体以及辅助桥联配体构筑的一类分子磁性体系，对其磁性的研究在基础理论方面和实际应用方面都有非常重大的意义。我们分别采用4个不同的两性离子型羧酸配体(L1-L4)与N3ˉ离子和金属离子Mn(II)和Co(II)自组装得到6个配位聚合物{[Mn5(L1)2(N3)8(OH)2]·12H2O}n(1)、 {[Mn5(L1)2(N3)8(H2O)2](ClO4)2·6H2O}n (2)、[Mn3(L2)(N3)6(H2O)4] (3)、 [Co3(L1)(N3)6(H2O)5] (4)、[Mn3(L3)4(N3)(CH3CH2OH)(H2O)]ClO4·4H2O (5)、 [Co3(L2)4(N3)2(H2O)2]·4NO3 (6) (L1 = 1,2,4,5-四(4-羧基吡啶-1-亚甲基)苯, L2 = 二氯[1,1′-双(4-羧基苯基)-4,4′-联吡啶, L3 =氯化[4-((1-羧基苯基)-吡啶-3)苯甲酸)。配合物1和2结构中含有相似却独特的ABCCB桥联Mn(II)的叠氮-羧基桥交替链。对其磁性研究表明，链内形成了F/AF/AF'/AF'/AF的磁传递序列，并形成了S = 5/2的自旋基态(对于每个Mn5单元)并产生一维拓扑亚铁磁行为。该磁传递序列是之前未见报道的，为分子磁学研究提供了一个新的桥联体系。我们采用J1–J2–J3–J3–J2磁耦合模型分别对1和2的磁性数据拟合得到J1 = 0.40 cm−1((EO-N3)2桥), J2 = −2.89 cm−1((EO-N3)-(OCO)2), J3 = −5.38 cm−1((EO-N3)-(OCO)), g = 2.01；J1 = 0.33 cm−1, J2 = −3.12 cm−1, J3 = −4.84 cm−1, g = 2.01。配合物3和4的结构中含有相似的以AABAA桥联方式桥联的叠氮-羧基桥交替链，链与链之间分别由配体L2和L1连成两维层结构。对其磁性研究表明，[(EO-N3)(OCO)]和(EO-N3)2桥在Mn(II)离子之间传递反铁磁耦合，而[(EO-N3)(OCO)2]和(EO-N3)2桥在Co(II)离子之间传递铁磁耦合。对配合物3采用J1–J1–J2的磁性拟合模型拟合得到J1 = -2.61 cm-1((EO-N3)(OCO))，J2 = -2.26