A family of rare earth porous coordination polymers with different flexibility for CO₂/C₂H₄ and CO ₂/C₂H₆ separation

A family of new porous coordination polymers (PCPs) were prepared by the reaction of an acylamide modified ligand (H₃L) and RE(NO) ₃·xH₂O (RE = Y, La, Ce, Nd, Eu, Tb, Dy, Ho, and Tm). PXRD and single-crystal X-ray analyses of them revealed that, besides the La PCP, all other rare earth members gave isomorphous structures. The two types of structural toplogies obtained, although similar, differ in their alignment of acylamide functional groups and structural flexibility. Adsorption experiments and in situ DRIFT spectra showed that rigid frameworks have the typical microporous behavior and poor selective capture of CO₂ over C ₂H₄ and C₂H₆; however, the unique La-PCP with structural flexibility and close-packed acylamide groups has a high selective capture of CO₂ with respect to C₂H₆ or C₂H₄ at 273 K, especially at the ambient pressure area (0.1-1 bar).