Molecular Sieving of Acetylene from Carbon Dioxide in a Flexible-Robust Metal–Organic Framework with Local Dynamic Molecular Gates

Development of molecular sieves to efficiently separate C2H2/CO2 mixtures is industrially important but very challenging due to their almost identical molecular sizes and physicochemical properties. Herein, we report a flexible-robust microporous metal–organic framework (ZJUT-5a) with local dynamic molecular gates, showing efficient molecular sieving of C2H2 from CO2. ZJUT-5a has a dynamic small-pore window constructed by rotated pyrazole rings, serving as local dynamic molecular gates to govern the passage of C2H2 and CO2. This dynamic gate can be opened by C2H2 due to stronger interactions, leading to a gate-opening effect for high C2H2 adsorption, while excluding CO2 adsorption. ZJUT-5a exhibits molecular sieving of C2H2 from CO2, with high C2H2 uptake and C2H2/CO2 uptake ratio (125.9 cm3 g–1 and 72.9) at 298 K and 1 bar. The C2H2 gate-opening adsorption mechanism based on such local dynamic molecular gates is elaborated by a combination of single-crystal X-ray diffraction, solid-state NMR studies, and theoretical calculations. Breakthrough experiments verify its excellent capability to capture C2H2 but to exclude CO2 from C2H2/CO2 mixtures under ambient conditions, affording by far the highest dynamic selectivity (129.4) and C2H2 productivity (122.9 L kg–1) with 98.4% recovery. This work offers a new strategy for designing flexible-robust frameworks with local dynamic gates as ideal molecular sieves for gas separations.