Visualizing Structural Transformation and Guest Binding in a Flexible Metal–Organic Framework under High Pressure and Room Temperature

Understanding the
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 feature “gate-opening/gate-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 states before and
after the structural transformation as induced by 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/gate-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.