Introduction of functionality into a Tb(III)-organic framework via mixed-ligand strategy for selective C2H2 capture and ratiometric Cr(VI) detection

Abstract

Introduction of porosity and fluorescent properties into lanthanide metal–organic frameworks (MOFs) with rational design to achieve multifunctional use is of great significance from the energy and environmental viewpoint. In this study, a microporous Tb(III)-based MOF with the formula of {[Tb2(oba)3(Phen)2](DMF)2(H2O)4}n (1) was solvothermally prepared via using the mixed ligands of 1,10-phenanthroline (Phen) and 4,4′-oxybis(benzoic acid) (H2oba) as organic connecters. The structural evaluation results indicate that complex 1 is composed of binuclear Tb2(CO2)6(Phen)2 clusters which are extended by the oba2− ligands to afford a two-fold interpenetrated framework with one-dimensional microporous channels along the b-axis. Gas sorption studies show that the activated 1 demonstrates a high ideal adsorption solution theory (IAST) sorption selectivity of 7.4 toward C2H2 in a C2H2/CO2 gas mixture, which are further supported by the dynamic breakthrough experiments. The grand canonical Monte Carlo (GCMC) simulation results indicate that the synergistic effects of the H-bond interactions of C2H2 with oba2− ligands and the C–H···π interactions with Phen ligand contribute to the strong binding of the framework toward C2H2 molecules. What's more, the luminescent measurements reveal that the emission of 1 features both the characteristic peaks of Phen ligand and Tb(III) ion, which could be further applied as a self-calibrating sensor for the Cr(VI) detection in water. To the best of our knowledge, complex 1 represents the first example of Tb-MOF holding such a high C2H2/CO2 selectivity together with ratiometric Cr(VI) detection performances.