Three-dimensional metal–organic frameworks (MOFs) containing substituted diimide ligands: synthesis, structures and gas sorption studies

Abstract

We report the synthesis, structures and gas sorption studies of two three-dimensional (3D) metal–organic frameworks (MOFs) namely {[Zn₂(OBZ)₂L1]·4DMF}_n (1) and {[Co₃(TER)₃(L2)(DMF)]·5DMF}_n (2), where OBZ²⁻ is deprotonated 4,4′-oxybis(benzoic acid), TER²⁻ is deprotonated terephthalic acid, DMF is N,N-dimethylformamide, L1 is 2,2′-bis(pyridin-3-ylmethyl)-[5,5′-biisoindoline]-1,1′,3,3′-tetraone and L2 is 5,5′-carbonylbis(2-(pyridin-3-ylmethyl)isoindoline-1,3-dione). 1 and 2 are 3D MOFs containing 2D channels. The desolvated phases of 1 and 2 (1-d and 2-d) adsorb modest amounts of carbon dioxide (CO₂) at 195 K and 273 K; however, 1-d displays stepwise adsorption of CO₂ at 195 K and hysteretic desorption. Notably, a gate-opening effect is triggered after 1-d adsorbs 63 cm³ (STP) g⁻¹, allowing the structure to open and adsorb an additional 54 cm³ (STP) g⁻¹. In contrast, 1-d adsorbs relatively small amounts of hydrogen (H₂) and nitrogen (N₂) gases, 3 cm³ (STP) g⁻¹ and 12 cm³ (STP) g⁻¹, respectively, suggesting selectivity of CO₂ over H₂ and N₂.