Two Structurally Similar Co5 Cluster-Based Metal-Organic Frameworks Containing Open Metal Sites for Efficient C2H2/CO2 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 [H4L = 2,6bis( 2 ', 5 '-dicarboxyphenyl)pyridine], [(NH2Me2)2]-[Co5(L)2(OCH3)2(mu 3-OH)2 center dot 2DMF]center dot 2DMF center dot 2H2O (1) and [Co5(L)2(mu 3-OH)2(H2O)2]center dot 2H2O center dot 4DMF (2). The structures of 1 and 2 are built from Co5 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 C2H2 (144.0 cm3 g-1 for 1 and 141.3 cm3 g-1 for 2), but 1 has a higher C2H2/CO2 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.

Automated summary

When designing and synthesizing metal-organic frameworks (MOFs) with high stability and excellent adsorption/separation performance, the pore configuration and functional sites play a crucial role. In this study, two structurally similar cluster-based MOFs were reported, with different microporous environments but both exhibiting extremely high chemical stabilities and similar C2H2 adsorption capacities. One of the MOFs showed higher C2H2/CO2 selectivity under ambient conditions. A combination of breakthrough experiment and theoretical calculation was used to compare the gas adsorption and separation performance of the two MOFs, and the influence of the microporous environment on MOFs performance was further studied.