Highly selective fluorescent probe for Hg²⁺ and MnO₄ ⁻ by the two-fold interpenetrating metal-organic framework with nitro functionalized linkers

A novel nitro functionalized Co(II) based two-fold interpenetrating metal-organic framework (MOF), [Co(NPDC)(bpee)]·DMF·2H₂O (1) (NPDC = 2-nitro phenylenedicarboxylate, bpee = 1,2-bis(4-bipyridyl)ethylene) has been synthesized by solvothermal method and structurally characterized. The complex consists of a 3D structure in which the nitro functionalized ligand (NPDC) and bipyridine type linkers (bpee) coordinated to Co(II), leading to a fsc type 3,5-c binodal net. The complex shows fluorescent emission both in solid state and in aqueous solution. What's more, it exhibits a high selectivity for the sensing of MnO₄ ⁻ and heavy metal ion Hg²⁺ in water by quenching or enhancing luminous intensity, respectively. Naked eyes can even recognize the changes in fluorescence intensities. This work represents a new approach for design and fabrication of functionalized metal-organic frameworks decorated with the nitro group in pore channels, induced by the pre-modified method. Moreover, the detection of Hg²⁺ and MnO₄ ⁻ indicates the opportunities of the complex be prominent fluorescent probes in potential applications. A new 3D nitro functionalized Co(II) based two-fold interpenetrating metal-organic framework was synthesized and structurally characterized. Photoluminescence study of the complex exhibits ligand-based emission in the solid state and aqueous medium. Moreover, fluorescence titration experiments reveal that the complex is highly selective for MnO₄ ⁻ by luminescence quenching effect and Hg²⁺ with exclusively enhanced luminescence. The study demonstrates that the potential application of MOFs as luminescent sensors via a pre-modified ligands strategy.