基于三氰合铁的磁双稳态材料的合成与表征

近年来，具有金属间电子转移特性的氰根桥连配合物因表现出对温度、磁场、压强及光等外界因素的双稳态响应成为分子磁学及磁性材料领域一个重要的研究热点。基于其简单易行的构筑块策略和丰富的调控手段，大量的研究结果表明其电子转移特性（比如发生温度、转变速度及热滞回线等）与分子间作用力、客体分子、抗衡阴离子、分子结构畸变、卤键等息息相关。

本论文主要基于不同的多吡唑三氰合铁构筑基元，与过渡金属离子（Co(II)或Fe(II)）及螯合配体dptrz或2, 9-二甲基-4, 7-二苯基-1, 10-菲咯啉（BCP）通过自组装构筑了20例不同的氰根桥连配合物(1-20)，研究了其结构、磁性及两者的关系，结果如下：

首先，基于位阻较大的BCP配体构筑了配合物1-7，其中配合物2-5具有氰根桥连的[Fe^III₂Co^II₂]平面四方结构，配合物1，6，7均为平面六核[Fe^III₄M^II₂]结构（M = Co, Fe, Ni）。值得注意的是，所有配合物中二价金属离子均采用五配位变形四棱锥构型，直流和交流磁化率研究表明均未表现出单分子磁体的行为。其中配合物3在100-150 K之间表现出类似电子转移的磁转变行为。

其次，基于配体dptrz构筑了氰根桥连Fe-Co配合物8-17。其中配合物11，12和14为[Fe^III₂Co^II]三核结构，13为[Fe^III₂Co^II₄]六核结构，而其他均为[Fe₂Co₂]平面四方结构。其中配合物8和9都表现出典型的电子转移行为，其电子转移温度分别在350 K和140 K。配合物15和16与配合物9具有相同的分子骨架而不同的抗衡阴离子，研究发现其电子转移温度分别移向210 K和125 K，说明抗衡阴离子对其电子转移行为具有显著的作用。同样，配合物17电子转移温度为370 K，略高于配合物8；有趣的是，配合物17在脱溶剂后表现出显著的负热膨胀效应。

另外，还得到一系列基于三氰合铁构筑基元的二维磁有序配合物，其中配合物18为铁磁体，而配合物19和20为亚铁磁体。

Recently, cyanide-bridged complexes with intermetallic electron transfer properties have been become an important research hotspot in the field of molecular magnetism and magnetic materials because of their bistable responses to external factors such as temperature, magnetic field, pressure, and light. Based on its simple and feasible building block strategy and abundant control methods, a large number of research results have shown that its electron transfer characteristics (such as occurrence temperature, transition speed and thermal hysteresis loop, etc.) are closely related to intermolecular forces, guest molecules, counter anions, molecular structure distortion, halogen bonds, and so on.

In this paper, 20 different cyanide bridged complexes (1-20) were constructed by transition metal ions (Co(II), Ni(II) or Fe(II)), chelating ligands (dptrz or BCP), and different polypyrazole tricyanoferric building blocks via self-assembly. Their structures, magnetism anf the relationship between the two have been studied, and the results are as follows:

Firstly, complexes 1-7 are constructed by ligand BCP which has a large steric hindrance. Complexes 2-5 have a cyanide-brdged [Fe^III₂Co^II₂] planar tetragonal structure, and complexed 1, 6 and 7 are all planar hexanuclear [Fe^III₄M^II₂] structures. Complexes 2 and 5 have a tendency of electron transfer at very low temperature (less than 30 K). It is worth noting that the divalent metal ions in all complexes adopt the five-coordinate deformed quadrangular pyramid configuration. Among them, complex 3 exhibits an electron transfer-like magnetic transition behavior between 100 and 150 K.

Secondly, cyanide-bridged Fe-Co complexes 8-17 were constructed based on the ligand dptrz. Complexes 11, 12 and 14 are [Fe^III₂Co^II] trinuclear molecules, 13 is [Fe^III₂Co^II₄] hexanuclear molecules, and the others are [Fe₂Co₂] planar tetragonal molecules. Among them, both complexes 8 and 9 exhibit typical electron transfer behavior, and their electron transfer temperatures are 350 K and 140 K, respectively. Compared with complex 9, complexes 15 and 16 have the same molecular skeleton but different counter anions. It’s found that their electron transfer temperatures shift to 210 and 125 K, respectively, indicating that the counter anions have a significant effect on their electron transfer behavior. Liskewise, the electron transfer temperature of complex 17 is 370 K, which is slightly higher than that of complex 8; interestingly, it exhibits a significant negative thermal expansion effect after desolvation.

In addition, we also obtained a series of two-dimensional magnetically ordered complexes based on the tricyanoferrate building block, in which complex 18 is a ferromagnet, while complexes 19 and 20 are ferrimagnets.

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