Effective luminescence sensing of Fe, CrO, MnO and 4-nitrophenol by lanthanide metal-organic frameworks with a new topology type.

Lanthanide MOFs (Ln-MOFs), {[Ln(L)(HO)]·5HO·6DMAC}, [Ln = Eu(1) and Tb(2); HL = 4,4'-(((5-carboxy-1,3-phenylene)bis(azanediyl))bis(carbonyl)) dibenzoic acid, DMAC = N,N'-dimethylacetamide], with a new topology type have been isolated. Single crystal X-ray diffraction indicates that complexes 1 and 2 are isostructural with binuclear [Eu(COO)] secondary building units as 7-connected nodes and HL ligands as 3-connected nodes and can be viewed as a (5,7)-connected 3D framework with a new topological point symbol of {3·4·5} {3·4·5·6}. Complexes 1 and 2 exhibit an excellent luminescence sensing response to inorganic ions Fe, CrO, MnO and 4-nitrophenol, with a low detection limit and high K value. Interestingly, when the MnO ions are detected, the color of the solid sample is observed to change from yellow to brown, visually indicating luminescence induction, which makes the process of detecting MnO ions simpler and more practical. Moreover, by using time-resolved photoluminescence techniques, complex 1 can effectively eliminate background fluorescence interference during detection and improve detection accuracy. Solvent luminescence studies, pH stability and PXRD data indicate that complexes 1 and 2 can be used as excellent water-stable multi-response luminescent sensors for detecting a wide variety of toxic substances. In addition, the mechanism of selective detection is explained by the energy competition between the excitation of complexes 1 and 2 and the ultraviolet absorption of the responsive substance.