Optimal Host-Guest Fit in Metal-Organic Frameworks to Achieve Record C2H2 Packing Density for Trace Acetylene Capture.

Host-guest fit is critical in enzyme-substrate binding and useful for designing crystalline porous adsorbents to remove trace impurities; however, realization of such remains highly scarce, let alone to elucidate the atomic-level understanding on how to optimize such an effect. Herein, we demonstrate the systematic design of a pillared-layer MOF series (CPL-1) to achieve optimal host-guest fit through increasing the number of bulky groups, progressively enhancing the C2H2 adsorption performance. The newly synthesized, best-fit SXU-10 exhibits the most superior very-low-pressure C2H2 capture-reaching near saturation at just 2 kPa. With record C2H2 packing densities of 483.9 mg cm-3 at 1 kPa and 733.97 mg cm-3 at 100 kPa, SXU-10 exhibits an uptake of 1.18 mmol g-1 C2H2 at 1 kPa and C2H2/C2H4 selectivity of 133 for 1/99 C2H2/C2H4 mixtures (all at 298 K), along with exceptional stability and humidity tolerance, enabling the production of polymer-grade C2H4 from trace C2H2 mixtures under a challenging humid condition (80% RH). The unusual steep-rise-uptake phenomenon and significantly improved performance are attributed to the optimized host-guest shape fit at a sub-ångström precision which constrains the gate-opening flexibility, evidenced via in situ single-crystal X-ray diffraction. The present study sheds light on the molecular-level engineering of bioinspired porous adaptive materials.