Luo Yu, Zhou Ren-He, Shao Zhen, Liu Dan, Lu Han-Han, Shang Meng-Jia, Zhao Liang, Liu Tao, Meng Yin-Shan
State Key Laboratory of Fine Chemicals, Frontier Science Center for Smart Materials, School of Chemical Engineering, Dalian University of Technology, 2 Linggong Road, Dalian 116024, China.
Dalton Trans. 2024 Sep 10;53(35):14692-14700. doi: 10.1039/d4dt01103a.
Spin crossover (SCO) has long been a hot topic in the field of molecular magnetism owing to its unique bistability character. Rational control of thermal hysteresis and transition temperature () is crucial for their practical applications, which rely on precise manipulation of the substituents of SCO coordinating ligands and molecular packing interactions. In this study, we designed two different bridging ligands (2-FDPB: 4,4'-(2-fluoro-1,4-phenylene)dipyridine; 2,3-FDPB: 4,4'-(2,3-difluoro-1,4-phenylene)dipyridine) featuring one and two fluoro substitution on the central benzene ring and applied a Schiff base-like equatorial tetradentate ligand {diethyl(,)-2,2'-[4,5-difluoro-1,2-phenyl-bis(iminomethylidyne)]bis(3-oxobutanoate)-(2-)-,',O3,O3'} (HL) to coordinate with the Fe ion. Two Fe-coordination chain polymers [Fe(L)(2,3-FDPB)]·0.25CHCl (1) and [Fe(L)(2-FDPB)]·0.5CHOH (2) were obtained. 1 crystallizes in the monoclinic 2/ space group with only one Fe center, while 2 crystallizes in the triclinic 1̄ space group with two independent Fe centers. Unlike the identical 2D layer stacking in 1, 2 exhibited alternating stacking of the extending 2D layers and meshed chains. Magnetic measurements revealed the typical thermally induced spin crossover behavior (SCO): 1 exhibited a 41 K-wide thermal hysteresis with transition temperatures of = 245 K and = 204 K, while 2 showed a higher transition temperature ( = 330 K) with no thermal hysteresis. Magneto-structural correlation studies suggest that the electron-withdrawing effect present in the fluoro substituents does not have a significant impact on the SCO behaviors. Despite the fluoro substituents having a similar atomic radius of hydrogen atoms, variations in the number of these substituents can alter the crystallization behavior of these complexes, which in turn affects the solvents, molecular stacking patterns, and intermolecular interactions, ultimately influencing the SCO behaviors.
自旋交叉（SCO）由于其独特的双稳态特性，长期以来一直是分子磁学领域的热门话题。对热滞回和转变温度（）进行合理控制对于其实际应用至关重要，这依赖于对SCO配位配体的取代基和分子堆积相互作用的精确调控。在本研究中，我们设计了两种不同的桥联配体（2-FDPB：4,4'-(2-氟-1,4-亚苯基)二吡啶；2,3-FDPB：4,4'-(2,3-二氟-1,4-亚苯基)二吡啶），其中心苯环上分别有一个和两个氟取代，并应用了一种席夫碱样的赤道四齿配体{二乙基(,)-2,2'-[4,5-二氟-1,2-苯基-双(亚氨基次甲基)]双(3-氧代丁酸酯)-(2-)-,',O3,O3'}（HL）与铁离子配位。得到了两种铁配位链聚合物[Fe(L)(2,3-FDPB)]·0.25CHCl（1）和[Fe(L)(2-FDPB)]·0.5CHOH（2）。1以单斜2/空间群结晶，只有一个铁中心，而2以三斜1̄空间群结晶，有两个独立的铁中心。与1中相同的二维层堆叠不同，2表现出延伸的二维层和网状链的交替堆叠。磁性测量揭示了典型的热诱导自旋交叉行为（SCO）：1表现出41 K宽的热滞回，转变温度= 245 K和= 204 K，而2显示出更高的转变温度（= 330 K）且没有热滞回。磁结构相关性研究表明，氟取代基中存在的吸电子效应对SCO行为没有显著影响。尽管氟取代基的原子半径与氢原子相似，但这些取代基数量的变化会改变这些配合物的结晶行为，进而影响溶剂、分子堆积模式和分子间相互作用，最终影响SCO行为。
