Construction of three-dimensional metal–organic frameworks in the presence of a tetrahedral ligand and a secondary bidentate linker

Abstract

Three microporous coordination polymers, namely, [Co₂L(DPE)]·2DMF·5H₂O (1), [Zn₂L(DPE)]·2.5DMF·2H₂O (2) and [Cd(H₂L)]·3DMF·3.5H₂O (3), were solvothermally prepared in the presence of the flexible tetrahedral carboxylate ligand tetrakis[(4-carboxyphenyl)oxamethyl]methane acid (H₄L) and a secondary bidentate linker (E)-1,2-di(pyridin-4-yl)ethane (DPE). Compounds 1 and 2 are isostructural and possess a 2-fold interpenetrating (4,4)-pts network. Compound 3 has a 3D structure with a uninodal 4-connected {4.8⁵} topology. All the three compounds consist of large solvent-accessible voids, but only compounds 1 and 2 possess permanent porosity as confirmed by N₂, CO₂ and CH₄ gas adsorption measurements. In addition, compounds 2 and 3 exhibited strong photoluminescent emissions at room temperature with a peak at 495 and 440 nm, respectively, owing to a ligand-centered excited state. The emission intensities of 2 varied upon contact with different solvents or analytes.