Two Stable Zn-Cluster-Based Metal–Organic Frameworks with Breathing Behavior: Synthesis, Structure, and Adsorption Properties

Two stable Zn-cluster-based MOFs, [Zn9(btz)12(atdbc)3(DMF)]·3DMF·12H2O (compound 1, Hbtz = 1H-benzotriazole, H2atdbc = 4,4′-(4-amino-1,2,4-triazol-3,5-diyl)dibenzoic acid, DMF = N,N-dimethylformamide) and [Zn4(btz)6(bcpt)]·3DMF (compound 2, H2bcpt = 3,5-bis(4′-carboxy-phenyl)-1,2,4-triazole), have been successfully constructed by adopting the mixed ligands approach. Both the compounds exhibit high chemical stability under aqueous solution and common organic solvents. Especially, compounds 1 and 2 can be stable in pH = 2 and pH = 12 solutions. Meanwhile, compound 1 exhibits good ability to selectively separate CO2 from CH4. CO2 over CH4 selectivity is 5.2 (0.5/0.5) and 5.7 (0.05/0.95) at 298 K under 1 bar, respectively, which may be used for the separation of gases in industrial applications. Moreover, compound 1 displays breathing behavior for small-molecule gases (N2, CO2, C2H6, and C3H8), and compound 2 only exhibits the same phenomenon for CO2 adsorption because of its ultramicroporous channels.