Visualizing Structural Transformation and Guest Binding in a Flexible Metal–Organic Framework under High Pressure and Room Temperature
Hui Yang, Feng Guo, Prem Lama, Gaurav Verma, Wen-Yang Gao, Hui Wu, Leonard J. Barbour, Wei Zhou, Jian Zhang, Briana Aguila, Shengqian Ma
Understanding effect of gas molecules on the framework structures upon gas sorption in porous materials is highly desirable for the development of gas storage and separation technologies. However, this remains challenging for flexible metal-organic frameworks (MOFs) which features "gate opening/closing" or "breathing" sorption behaviors under external stimuli. Herein, we report such a flexible Cd-MOF that exhibits "gating effect" upon CO2 sorption. The ability of the desolvated flexible Cd-MOF to retain crystal singularity under high pressure enables the direct visualization of the reversible closed/open-pore structure transformation as induced by the CO2 adsorption/desorption through in situ single crystal X-ray diffraction experiments. The binding sites of CO2 molecules within the flexible MOF under high pressure and room temperature have also been identified via combined in situ single crystal X-ray diffraction and powder X-ray diffraction studies, facilitating the elucidation of the states observed during gate opening/closing behaviors. Our work therefore lays a foundation to understand the high-pressure gas sorption within flexible MOFs at ambient temperature, which will help to improve the design efforts of new flexible MOFs for applications in responsive gas sorption and separation.