Neutral Molecular Iron(II) Complexes Showing Tunable Bistability at Above, Below, and Just Room Temperature by a Crystal Engineering Approach: Ligand Mobility into a Three-Dimensional Flexible Supramolecular Network
Neutral Molecular Iron(II) Complexes Showing Tunable Bistability at Above, Below, and Just Room Temperature by a Crystal Engineering Approach: Ligand Mobility into a Three-Dimensional Flexible Supramolecular Network
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DOI：
10.1021/acs.cgd.7b01141
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发表时间：
2017-11-01
影响因子：
3.8
通讯作者：
Murai, Kei-ichiro
中科院分区：
文献类型：
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作者：
Hagiwara, Hiroaki;Masuda, Takuya;Murai, Kei-ichiro
室温（RT）双稳态开关材料一直吸引着科学家们，因为它们可用于一类新型的基于分子的开关或存储器。虽然自旋交叉（SCO）化合物属于这些有吸引力的材料，但以合理的方式设计出具有理想双稳态（即跨越室温的宽滞后环）的SCO系统仍然是一个极具挑战性的问题。在此我们报道了一类新的中性分子铁（II）配合物，其在跨越室温的宽范围开关温度（239 - 409 K）和滞后宽度（1 - 31 K）内呈现出滞后的SCO现象。这些材料是以两种无溶剂化合物[Fe - II(ptm(2)-dmpn)(NCS)₂]（1；ptm(2)-dmpn = N,N'-双[(1 - 苯基 - 1H - 1,2,3 - 三唑 - 4 - 基)亚甲基]-2,2 - 二甲基丙烷 - 1,3 - 二胺）和[Fe - II(p - ttm(2)-dmpn)(NCS)₂]（2；p - ttm(2)-dmpn = N,N'-双[(1 - 对甲苯基 - 1H - 1,2,3 - 三唑 - 4 - 基)亚甲基]-2,2 - 二甲基丙烷 - 1,3 - 二胺）的单晶形式获得的，以及两种溶剂化物[Fe - II(p - ttm(2)-etpn)(NCS)₂]·溶剂（p - ttm(2)-etpn = N,N'-双[(1 - 对甲苯基 - 1H - 1,2,3 - 三唑 - 4 - 基)亚甲基]-1 - 乙基丙烷 - 1,3 - 二胺，溶剂分别为0.5H₂O和0.5MeCN·0.5MeOH·H₂O，对应3a和3b）。所有化合物都由一个三维（3D）柔性超分子网络构成，通过多个弱的C - H···S氢键，并通过四齿配体相邻芳环之间的芳香相互作用（即π - π和C - H···π相互作用）包含一个额外的有序维度结构。这些3D网络能够容纳多种分子运动，例如（1）NCS弯曲，（2）四齿配体咬合，（3）芳环旋转，以及（4）丙烯片段振荡，其程度因小烷基取代基和晶格溶剂的微小改变而有所不同。目前这种将协同多分子运动引入3D柔性网络的晶体工程方法可以成为一种新的设计理念，用于以系统的方式控制开关温度和协同性，以发现前所未有的室温双稳态SCO材料。
Room temperature (RT) bistable switching materials continue to fascinate the scientists since they can be utilized for a new class of molecular-based switches or memories. While the spin crossover (SCO) compound is categorized into these attractive materials, designing of a SCO system showing desirable bistability (i.e., wide hysteresis loop spanning RT) in a rational way is still a very challenging issue. We report herein a new family of neutral molecular iron(II) complexes showing hysteretic SCO in a wide range of switching temperatures (239-409 K) and hysteresis widths (1-31 K) spanning RT. These materials were obtained as single crystals of two solvent-free compounds [Fe-II(ptm(2)-dmpn)(NCS)(2)] (1; ptm(2)-dmpn = N,N '-bis[(1-phenyl-1H-1,2,3-triazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine) and [Fe-II(p-ttm(2)-dmpn)(NCS)(2)] (2; p-ttm(2)-dmpn = N,N '-bis[(1-p-tolyl-1H-1,2,3-triazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine), and two solvatomorphs [Fe-II(p-ttm(2)-etpn)(NCS)(2)]center dot solvent (p-ttm(2)-etpn = N,N '-bis[(1-p-tolyl-1H-1,2,3-triazol-4-yl)methylene]-1-ethylpropane-1,3-diamine, and solvent = 0.5H(2)O and 0.5MeCN center dot 0.5MeOH center dot H2O for 3a and 3b, respectively). All compounds are constructed of a three-dimensional (3D) flexible supramolecular network by multiple weak CH center dot center dot center dot S hydrogen bonds incorporating an additional orderly dimensional structure by aromatic interactions (i.e., pi-pi and CH center dot center dot center dot pi interactions) between adjacent aromatic rings of tetradentate ligands. These 3D networks can accommodate a number of molecular motions such as (1) NCS bending, (2) tetradentate ligand biting, (3) aromatic ring rotation, and (4) propylene fragment oscillation to various degrees depending on a slight modification of small alkyl substituents and lattice solvents. The present crystal engineering approach of introducing concerted multimolecular motions into a 3D flexible network can be a new designing concept for controlling switching temperature and cooperativity in a systematic way toward the discovery of unprecedented RT bistable SCO materials.