High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages
High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages
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DOI：
10.1073/pnas.1504586112
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发表时间：
2015-11-17
影响因子：
11.1
通讯作者：
Kim, Kwang S.
中科院分区：
文献类型：
--
作者：
Baek, Seung Bin;Moon, Dohyun;Kim, Kwang S.
由于吸附气体分子的快速运动，晶体学观察是一项非常困难的任务。在这里，我们报告在原位单晶和同步加速器粉末X射线观测的可逆CO2吸附过程中，在不同的压力下，在高温下，在一个明显的无孔有机晶体。主体材料由1，3，5-三-（4-羧基苯基）苯（H3 BTB）和N，N-二甲基甲酰胺（DMF）之间的氢键网络以及H3 BTB部分之间的π-π堆积形成。该材料可以被看作是一个有序的笼阵列，这些笼彼此紧密堆积，使得笼从外部无法接近。因此，宿主实际上是无孔的。尽管没有永久的途径连接空笼子，他们是可渗透的CO2在高温下，由于热激活的分子门控，和弱限制的CO2分子在笼子里允许直接检测原位单晶X-射线衍射在323 K。变温原位同步辐射粉末X射线衍射研究也表明，CO2吸附是可逆的，由温度升高驱动。固态魔角旋转NMR定义了CO2与有机骨架的相互作用以及CO2在笼中的动态运动。可逆吸附归因于DMF分子的动态运动与CO2的轴向运动/角度波动（一系列使CO2分子通过的隔室的瞬时打开/关闭）的组合，如从NMR和模拟所揭示的。这种温度驱动的瞬态分子门控可以将气体分子以有序阵列存储到独特的集体性质，并释放它们以备使用。
Crystallographic observation of adsorbed gas molecules is a highly difficult task due to their rapid motion. Here, we report the in situ single-crystal and synchrotron powder X-ray observations of reversible CO2 sorption processes in an apparently nonporous organic crystal under varying pressures at high temperatures. The host material is formed by hydrogen bond network between 1,3,5-tris-(4-carboxyphenyl) benzene (H3BTB) and N,N-dimethylformamide (DMF) and by pi-pi stacking between the H3BTB moieties. The material can be viewed as a well-ordered array of cages, which are tight packed with each other so that the cages are inaccessible from outside. Thus, the host is practically nonporous. Despite the absence of permanent pathways connecting the empty cages, they are permeable to CO2 at high temperatures due to thermally activated molecular gating, and the weakly confined CO2 molecules in the cages allow direct detection by in situ single-crystal X-ray diffraction at 323 K. Variable-temperature in situ synchrotron powder X-ray diffraction studies also show that the CO2 sorption is reversible and driven by temperature increase. Solid-state magic angle spinning NMR defines the interactions of CO2 with the organic framework and dynamic motion of CO2 in cages. The reversible sorption is attributed to the dynamic motion of the DMF molecules combined with the axial motions/angular fluctuations of CO2 (a series of transient opening/closing of compartments enabling CO2 molecule passage), as revealed from NMR and simulations. This temperature-driven transient molecular gating can store gaseous molecules in ordered arrays toward unique collective properties and release them for ready use.