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

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.