A Zn(ii) metal–organic framework constructed by a mixed-ligand strategy for CO2 capture and gas separation

Abstract

By introducing the 1,2,4-triazole ligand in the tetracarboxylate system, an anionic metal–organic framework [(CH₃)₂NH₂][Zn₂(ABTC)(Tz)]·3DMF (compound 1, ABTC = 2,2′,5,5′-azobenzene tetracarboxylic acid, Tz = 1,2,4-triazole and DMF = N,N-dimethylformamide) was synthesized under solvothermal conditions. There were two types of inorganic secondary building units (SBUs) in compound 1, i.e., a classical Zn-paddlewheel [Zn₂(COO)₄] and a metal cluster of [Zn₂(Tz)₂(COO)₄], which were linked by ABTC⁴⁻ to form a 3D porous framework. Because of the two inorganic SBUs as 6-connected nodes and ABTC⁴⁻ as 4-connected nodes, compound 1 could be simplified to with a point symbol of (3²·6²·7²) (3⁴·4²·6⁴·7⁵). Compound 1 displayed CO₂ adsorption capacity of 92.1 cm³ g⁻¹ at 273 K under 1 atm. Furthermore, 1 exhibited good adsorption capacity for small molecular gases (CH₄, C₂H₆ and C₃H₈) and excellent separation selectivity for CO₂/CH₄, C₂H₆/CH₄ and C₃H₈/CH₄.