Regulation of the pore size by shifting the coordination sites of ligands in two MOFs: enhancement of CO2 uptake and selective sensing of nitrobenzene

Abstract

Two metal–organic frameworks (MOFs), namely {[Cd₂(sdb)₂(4-bpmh)₂(H₂O)]}_n·2n(H₂O) (1), {[Cd₂(sdb)₂(3-bpmh)₂]}_n·3n(H₂O)·n(C₆H₅NO) (2), [sdb = 4,4′-sulfonyl dibenzoic acid; 4-bpmh = N,N-bis-pyridin-4-ylmethylene-hydrazine, 3-bpmh = N,N-bis-pyridin-3-ylmethylene-hydrazine, C₆H₅NO = 3-pyridinecarboxaldehyde] have been synthesized by the solvent diffusion technique at room temperature. Structure determination reveals that compound 1 has 2D interdigitated architectures, whereas 2 is a 2-fold interwoven 3D porous network but both 1 and 2 have a common secondary building unit (SBU) [Cd₂(sdb)₄(L)₄] [L = 4-bpmh (1) and 3-bpmh (2)]. Gas adsorption studies demonstrate that compound 2 shows high selectivity for CO₂ over CH₄ and the uptake amounts are almost double in comparison with compound 1 and both the compounds show high sensitivity for nitrobenzene via the fluorescence quenching mechanism.