Two 2D microporous MOFs based on bent carboxylates and a linear spacer for selective CO2 adsorption

Abstract

Two new 2D MOFs, formulated as {[Cd(OBA)(L)]·DMF}_n, 1 and {[Zn₂(SDB)₂(L)]·EtOH·3H₂O·2DMF}_n, 2 (L = 3-pyridinecarboxaldehyde nicotinoylhydrazone, H₂OBA = 4,4′-oxybis(benzoic acid), H₂SDB = 4,4′-sulfonyldibenzoic acid, DMF = N,N-dimethylformamide), have been synthesized at room temperature and characterized by elemental analyses (EA), FTIR spectra, single-crystal X-ray diffraction analyses (SCXRD), powder X-ray diffraction analyses (PXRD) and thermogravimetric analyses (TGA). The structural investigations reveal that both MOFs can be rationalized as a 4-c, uninodal net with sql topology. 1 and 2 are permanently microporous, having 1D channels with approximate sizes of 3.6 × 4.2 Ų and 6.6 × 8.0 Ų, respectively. Furthermore, CO₂, CH₄ and N₂ sorption studies are carried out in detail at varying temperatures, and the results show that the adsorption capacities of both 1 and 2 towards CO₂ are higher than those towards CH₄ and N₂. Importantly, IAST calculations reveal that 1 and 2 display high separation selectivities for CO₂/N₂ (15 : 85) and CO₂/CH₄ (50 : 50) mixtures at ambient conditions.