基于四嗪自由基桥连的双稳态分子磁体的研究

STUDY ON BISTABLE MOLECULAR MAGNETS BASED ON TETRAZINE RADICAL BRIDGE

战鹏志

11849425

硕士

化学

张元竹

2020-05-30

2020-07-09

哈尔滨工业大学

深圳

单分子磁体领域经过近三十年的发展， 在提高磁各向异性能垒及阻塞温度方面取得了令人振奋的成果。通过调控金属离子的配位构型以优化目标分子的自旋轨道耦合，实现单轴磁各向异性的最大化，成为构筑高性能单分子磁体的重要手段。 近几年研究发现利用自由基桥引入强的磁耦合作用可以有效抑制量子隧穿效应， 进一步提高弛豫时间。 四嗪类配体因其便于合成并可形成稳定的自由基开始受到人们的重视。本文设计合成了一系列四嗪基双三齿桥连配体，通过自组装的方式成功构筑了一系列双核，四核及多核的分子体系， 摸索了该类配体实现自由基可控转变的可行性，研究了这类配合物的结构和磁性及其对应关系， 相关工作如下：在不引入其他辅助配体的情况下， 通过四嗪类桥连配体与二价钴离子自组装 得 到 4 例 多 核 Co(II) 配 合 物 ： {[CoⅢ2(LBpy-O1)2][BPh4]2}•5CH3CN (1) 、{[CoⅢ2(LBpy-O1)2][ClO4]2}•5DMF (2) 、 {CoⅡ4(LBpy-O3)2(LBpy-O2)2[ClO4]6}•4CH3CN(3)、 {[CoⅢ2(LPhen-O1)2][BPh4]2}•5CH3CN (4)。 单晶结构研究发现， 在二价钴离子存在的情况下，该类四嗪配体被原位催化开环(LBpy-O1, LPhen-O1, LBpy-O2)或形成五元环(LBpy-O3)。通过引入三联吡啶类三齿螯合配体来调控过渡金属离子的配位环境，进一步 摸 索 四 嗪 自 由 基 形 成 的 可 行 条 件 ， 合 成 了 配 合 物 5-7 ：{[FeⅡ2(LBpy)(Tpy)2][CF3SO3]4}•3DMF (5) 、 [CoⅡ2(LBpy-O3)(Bpp)2][ClO4]4 (6) 、[CoⅡ2(LBpy-O3)(Tpy)2](CF3SO3)4 (7)。 其中，在配合物 5 中四嗪未发生开环， 磁性研究未观测 Fe(II)离子的自旋翻转现象。结合铁钴电子转移体系的实现条件，探索了四嗪开环配体桥连的双核体系与 三 氰 合 铁 构 筑 基 元 的 自 组 装 ， 合 成 了 两 例 多 核 铁 钴 配 合 物 ：{[(Tp)FeⅢ(CN)3]8[(Tp)FeⅡ(CN)3][CoⅡ6(LBpy-O3)3(DMF)3][CF3SO3]2}•13CH3CN (8)、{[(Tp*)FeⅢ(CN)3]4[CoⅡ2(LBpy-O3)]}•4CH3CN (9)， 两例化合物均无电子转移行为。

Significant progress including both the anisotropic energy barrier and blocking temperature have been achieved after nearly thirty years of development in the field of single-molecule magnets. A key underpinning of research on the construction of high-performance SMMs is the opportunity to maximize uniaxial maximized magnetic anisotropy through modulating the coordination geometry as well as the spin-orbit coupling of the target molecules. Research of SMMs in recent years indicate that strong exchange couplings mediated by the radical bridges can effectively suppress the QTM and increase the relaxation times, for which tetrazine-based ligands have attracted considerable attentions due to the ease of satisfying the requirement for convenient syhthesis and stable redox isomers. Here in we report the synthesis and magnetic studies of a series of binuclear, tetranuclear and polynuclear complexes through self-assembly between the different metal species and pre-designed tetrazine-based bis-tridentate bridging ligands. The details are as follows: Self-assembly of Co(II) salts and the tetrazine bridging ligands in the absence of other coligands afforded four polynuclear Co(II) complexes: {[Co2(LBpy-O1)2][BPh4]2}•5CH3CN (1), {[Co2(LBpy-O1)2][ClO4]2}•5DMF (2), {Co4(LBpy-O3)2(LBpy-O2)2[ClO4]6}•4CH3CN (3) and {[Co2(LPhen-O1)2][BPh4]2}• 5CH3CN (4). Single-crystal X-ray diffraction studies revealed that the tetrazine ligands has been catalyzed in situ as open-cyclic LBpy-O1, LPhen-O1, LBpy-O2 ligands or five-membered rings (LBpy-O3). Similar reactions in the presence of terpyridine coligands led to complexes {[Fe2(L4N-Bpy)(Tpy)2][CF3SO3]4}•3DMF (5), [Co2(LBpy-O3)(Bpp)2][ClO4]4 (6) and [Co2(LBpy-O3)(Tpy)2](CF3SO3)4 (7), among which the tetrazine units of 5 did not undergo the ring-opening process. No spin transition was observed for 5. Further attempts through the reaction between the open-cyclic dinuclear Co(II)units and tricyanoferric building blocks towards the electron transfer materials afforded another two polynuclear Fe-Co complexes: {[(Tp)Fe(CN)3]9[Co6(LBpy-O3)3] [CF3SO3]2}•13CH3CN (8) and {[(Tp*)Fe(CN)3]4[Co2(LBpy-O3)]}•4CH3CN (9). No electron transfer behavior was observed for both the complexes.

单分子磁体 四嗪桥连配体 自由基 四嗪开环

single-molecule magnet tetrazine bridging ligand free radical tetrazine ring opening

中文

联合培养

南方科技大学

战鹏志. 基于四嗪自由基桥连的双稳态分子磁体的研究[D]. 深圳. 哈尔滨工业大学,2020.