Selective Gas Adsorption in the Flexible Metal–Organic Frameworks Cu(BDTri)L (L=DMF, DEF)

Abstract Use of the ditopic ligand 1,4‐benzenedi(1 H ‐1,2,3‐triazole) (H 2 BDTri) enabled isolation of two new three‐dimensional metal–organic frameworks of formulae Cu(BDTri)L in which L=DMF ( 1 ) and diethylformamide (DEF; 2 ). These compounds have the same primary structure, featuring one‐dimensional channels with the bridging DMF or DEF molecules pointing into the cavity. Upon exposure to solvent vapors, both display a reversible flexibility, as characterized by single‐crystal to single‐crystal phase transitions in 1 . The O 2 adsorption isotherms for the compounds show a two‐step adsorption behavior associated with a permanent microporosity and a pore‐opening process. In the case of N 2 adsorption, only 1 exhibits a two‐step adsorption isotherm, whereas 2 does not present any pore opening, demonstrating that design of a flexible framework cavity can control the pore opening and thereby possibly enhance O 2 /N 2 separation.