A Stable Zr(IV)-Based Metal Organic Framework Constructed from C=C Bridged Di-isophthalate Ligand for Sensitive Detection of Cr2O72- in Water

As the Cr2O72- anion is highly toxic, new sensors have been developing for its effective detection from water, among which metal-organic frameworks (MOFs) show distinct superiority over many other materials. Herein, a new fluorescent Zr(IV)-based MOF, [Zr6O4(OH)(8)(H2O)(4)(sbtc)(2)] (referred to as BUT-28), based on the di-isophthalate ligand with a central CH=CH moiety, trans-stilbene-3,3',5,5'-tetracarboxylate (sbtc(4-)), has been prepared and structurally determined. The MOF shows excellent stability in neutral, highly acidic, and weakly basic aqueous solutions. Moreover, no essential uptake loss in three cycles of water vapor adsorption-desorption measurements was observed for BUT-28, suggesting the robustness of the porous framework and its great potential for long-term use. Fluorescent measurements were carried out for BUT-28 and an isostructural MOF, Zr-abtc, which is constructed from the di-isophthalate ligand with a central N=N moiety, azobenzene-3,3',5,5'-tetracarboxylate (abtc(4-)). Interestingly, Zr-abtc shows very weak fluorescent emission. In contrast, BUT-28 exhibits relatively strong fluorescence and serves as a promising sensory material for the detection of trace Cr2O72- (limit of detection: 36 ppb) in aqueous solutions by selective and sensitive fluorescence quenching effect.