Pang Qingqing, Tu Binbin, Yang Lingyi, Li Qiaowei
Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200438, China.
Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200438, China.
Sci Bull (Beijing). 2019 Dec 30;64(24):1881-1889. doi: 10.1016/j.scib.2019.10.001. Epub 2019 Oct 3.
Single crystallinity of metal-organic frameworks (MOFs) enables the studies of their flexible behaviors with atomic precision. Here, we investigated the structural transformations triggered by photochemical cycloaddition and with temperature-dependent breathing in a series of pillared-layer MOF structures using a variety of pyrazolecarboxylate linkers for the layers and bipyridyl linkers as the pillars. The ethylenic double bonds from the pillars in close proximity undergo quantitative and seteroselective photochemical [2 + 2] cycloaddition upon UV irradiation, transforming the MOFs into structures with cyclobutane-based pillars. Furthermore, reversible breathing of the new pillared-layer MOF was evidenced by the 10.8% unit cell parameter change along c axis upon temperature change between 298 and 173 K. As revealed by single crystal X-ray diffraction, this transformation originates from the relative flattening of the wavy layers upon cooling. These two different types of characteristic structural transformations responding to inherent reactions and external stimuli happen at single crystalline state, providing a well-defined robust system with controlled flexibility.
金属有机框架（MOF）的单晶性使得能够以原子精度研究其柔性行为。在此，我们使用一系列用于层的吡唑羧酸酯连接体和作为支柱的联吡啶连接体，研究了一系列柱状层MOF结构中由光化学环加成和温度依赖性呼吸引发的结构转变。在紫外线照射下，来自相邻支柱的烯键式双键发生定量和立体选择性的光化学[2 + 2]环加成，将MOF转变为具有基于环丁烷支柱的结构。此外，新的柱状层MOF在298 K和173 K之间温度变化时，沿c轴的晶胞参数变化10.8%，证明了其可逆呼吸。如单晶X射线衍射所示，这种转变源于冷却时波浪状层的相对变平。这两种响应固有反应和外部刺激的不同类型的特征结构转变发生在单晶状态，提供了一个具有可控柔性的明确稳健体系。
