Metal-Organic Frameworks Featuring 18-Connected Nonanuclear Rare-Earth Oxygen Clusters and Cavities for Efficient C2H2/CO2 Separation.

Two rare-earth (RE) metal-organic frameworks (MOFs) formulated as {(Me2NH2)2[RE9(μ3-OH)8(μ2-OH)3(DCPB)6(H2O)3]}n (RE = Y3+ and Tb3+; termed JXNU-10) built from a triangular 3,5-di(4'-carboxylphenyl)benzoic acid (DCPB3-) ligand are presented. JXNU-10 features the rarely observed 18-connected nonanuclear [RE9(μ3-OH)8(μ2-OH)3] clusters, one-dimensional-nanosized tubular channels, and trigonal-bipyramidal cavities. The presence of the high-nuclear RE-oxo clusters and the robust coordination bonds between the highly charged RE ions and the hard base of the carboxylate/hydroxyl oxygen atoms yielded the water-resistant JXNU-10 materials. JXNU-10 exhibits highly selective sorption of C2H2 over CO2 and highly efficient separation of a C2H2 and CO2 mixture. The carboxylate oxygen atoms and the rich π systems of the organic ligands on the pore walls are the desirable binding sites for a C2H2 molecule with acidic hydrogen atoms and an alkyne group, facilitating the excellent efficiency of JXNU-10 for C2H2/CO2 separation demonstrated by breakthrough experiments.