Tetracarboxylate Linker-Based Flexible CuII Frameworks: Efficient Separation of CO₂ from CO₂/N₂ and C₂H₂ from C₂H₂/C₂H₄ Mixtures

摘要

We report the synthesis, structure, and adsorption properties of two new metal–organic frameworks (MOFs) {[Cu_(2)(bpp)_(3)(L1 )]·(bpp)·(4H_(2)O)} (1 ) and {[Cu_(2)(bipy)_(2)(L2 )(H_(2)O)_(2)]·(bipy)·(5H_(2)O)} (2 ) obtained from two different flexible tetracarboxylate linkers (L1 and L2 ) of variable lengths and flexibility. While 1 comprising Cu~(II), L1 , and 1,3-bis(4-pyridyl) propane (bpp) is a 2D MOF with a cage-type structure, 2 consisting of Cu~(II), L2 , and 4,4′-bipyridine (bipy) has a 3D twofold interpenetrated structure. Both frameworks manifest permanent porosity, as realized from CO_(2) adsorption at 195 K. 2 shows excellent CO_(2)/N_(2) and C_(2)H_(2)/C_(2)H_(4) adsorption selectivity at 298 K. This has been established by using 2 as a separating medium in a breakthrough column for separating mixtures of CO_(2)/N_(2) (15:85, v/v) and C_(2)H_(2)/C_(2)H_(4) (1:99, v/v). The selectivity of 2 toward CO_(2) over N_(2) and C_(2)H_(2) over C_(2)H_(4) is governed by favorable thermodynamic interactions owing to its structural flexibility, unsaturated metal sites, and polar carboxylate groups. Thus, 2 proves to be an extremely efficient material for specific gas separation.