Anchoring Highly Unsaturated Nickel(II) Sites into a Metal-Organic Framework for Simultaneous High CH Adsorption and Separation.

Separation of acetylene (CH) from carbon dioxide (CO) remains a challenge to achieve both high CH 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 CH/CO 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@NOTT-101-(COOH)) for simultaneously improving CH adsorption and selectivity. The coordination geometry of the anchored Ni ion was accurately determined by SCXRD studies, featuring a two-coordination model with highly unsaturated OMSs after the activation. This highly unsaturated Ni ion can provide additional binding sites to improve CH adsorption and also enable highly selective binding of CH over CO 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 CH uptake (201.4 cm g) and CH/CO selectivity (25.7) than the pristine NOTT-101-(COOH) (148.0 cm g and 3.8) at 298 K and 1 bar, making an unprecedented balance between CH adsorption and selectivity to overcome the trade-off challenge. Breakthrough experiments on equimolar CH/CO mixtures afford both the top-tier dynamic selectivity (14.4) and CH productivity of 114.5 L kg (>99.5% purity) at ambient conditions.