Two Structurally Similar Co 5 Cluster-Based Metal-Organic Frameworks Containing Open Metal Sites for Efficient C 2 H 2 /CO 2 Separation.

To reasonably design and synthesize metal-organic frameworks (MOFs) with high stability and excellent adsorption/separation performance, the pore configuration and functional sites are very important. Here, we report two structurally similar cluster-based MOFs using a pyridine-modified low-symmetry ligand [H 4 L = 2,6-bis(2',5'-dicarboxyphenyl)pyridine], [(NH 2 Me 2 ) 2 ][Co 5 (L) 2 (OCH 3 ) 2 (μ 3 -OH) 2 ·2DMF]·2DMF·2H 2 O ( 1 ) and [Co 5 (L) 2 (μ 3 -OH) 2 (H 2 O) 2 ]·2H 2 O·4DMF ( 2 ). The structures of 1 and 2 are built from Co 5 clusters, which have one-dimensional open channels, but their microporous environments are different due to the different ways in which ligands bind to the metals. Both MOFs have extremely high chemical stabilities over a wide pH range (2-12). The two MOFs have similar adsorption capacities of C 2 H 2 (144.0 cm 3 g -1 for 1 and 141.3 cm 3 g -1 for 2 ), but 1 has a higher C 2 H 2 /CO 2 selectivity of 3.5 under ambient conditions. The difference in gas adsorption and separation between the two MOFs has been compared by a breakthrough experiment and theoretical calculation, and the influence of the microporous environment on the gas adsorption and separation performance of MOFs has been further studied.