Anchoring Highly Unsaturated Nickel(II) Sites into a Metal–Organic Framework for Simultaneous High C 2 H 2 Adsorption and Separation

Abstract Separation of acetylene (C 2 H 2 ) from carbon dioxide (CO 2 ) remains a challenge to achieve both high C 2 H 2 uptake and selectivity for a single material. Porous materials with open metal sites (OMSs) have been widely employed to separate various gas mixtures; however, routine OMSs often show the limitation in C 2 H 2 /CO 2 separation due to the comparable binding affinity with the two gases. Herein, we report a new strategy of anchoring highly unsaturated nickel(II) sites into a large‐pore MOF (Ni 2+ @NOTT‐101‐(COOH) 2 ) for simultaneously improving C 2 H 2 adsorption and selectivity. The coordination geometry of the anchored Ni 2+ ion was accurately determined by SCXRD studies, featuring a two‐coordination model with highly unsaturated OMSs after the activation. This highly unsaturated Ni 2+ ion can provide additional binding sites to improve C 2 H 2 adsorption and also enable highly selective binding of C 2 H 2 over CO 2 through the specific and strong π‐ complexation interactions, as revealed by gas‐loaded SCXRD studies and theoretical simulations. This metalated MOF thus exhibits both significantly enhanced C 2 H 2 uptake (201.4 cm 3 g −1 ) and C 2 H 2 /CO 2 selectivity (25.7) than the pristine NOTT‐101‐(COOH) 2 (148.0 cm 3 g −1 and 3.8) at 298 K and 1 bar, making an unprecedented balance between C 2 H 2 adsorption and selectivity to overcome the trade‐off challenge. Breakthrough experiments on equimolar C 2 H 2 /CO 2 mixtures afford both the top‐tier dynamic selectivity (14.4) and C 2 H 2 productivity of 114.5 L kg −1 (>99.5% purity) at ambient conditions.