Spatial disposition of square-planar mononuclear nodes in metal-organic frameworks for C 2 H 2 /CO 2 separation.

The efficient separation of acetylene (C 2 H 2 ) from its mixture with carbon dioxide (CO 2 ) remains a challenging industrial process due to their close molecular sizes/shapes and similar physical properties. Herein, we report a microporous metal-organic framework (JNU-4) with square-planar mononuclear copper(ii) centers as nodes and tetrahedral organic linkers as spacers, allowing for two accessible binding sites per metal center for C 2 H 2 molecules. Consequently, JNU-4 exhibits excellent C 2 H 2 adsorption capacity, particularly at 298 K and 0.5 bar (200 cm 3 g -1 ). Detailed computational studies confirm that C 2 H 2 molecules are indeed predominantly located in close proximity to the square-planar copper centers on both sides. Breakthrough experiments demonstrate that JNU-4 is capable of efficiently separating C 2 H 2 from a 50 : 50 C 2 H 2 /CO 2 mixture over a broad range of flow rates, affording by far the largest C 2 H 2 capture capacity (160 cm 3 g -1 ) and fuel-grade C 2 H 2 production (105 cm 3 g -1 , ≥98% purity) upon desorption. Simply by maximizing accessible open metal sites on mononuclear metal centers, this work presents a promising strategy to improve the C 2 H 2 adsorption capacity and address the challenging C 2 H 2 /CO 2 separation.