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) {[Cu2(bpp)3(>L1)]·(bpp)·(4H2O)} (>1) and {[Cu2(bipy)2(>L2)(H2O)2]·(bipy)·(5H2O)} (>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 CO2 adsorption at 195 K. >2 shows excellent CO2/N2 and C2H2/C2H4 adsorption selectivity at 298 K. This has been established by using >2 as a separating medium in a breakthrough column for separating mixtures of CO2/N₂ (15:85, v/v) and C₂H₂/C₂H₄ (1:99, v/v). The selectivity of >2 toward CO₂ over N₂ and C₂H₂ over C₂H₄ is governed by favorable thermodynamic interactions owing to its structural flexibility, unsaturated metal sites, and polar carboxylate groups. Thus, >2 proves to be an extremelyefficient material for specific gas separation.