Efficient luminescence sensing in two lanthanide metal–organic frameworks with rich uncoordinated Lewis basic sites

Abstract

Developing highly sensitive MOF-based probes for environmental contaminant detection is of much importance and challenging. Here, two new three-dimensional lanthanide metal–organic frameworks (Ln-MOFs), {[Eu(DTA)_1.5(H₂O)]·H₂O}_n (Eu-DTA) and [Tb(DTA)(C₂O₄)_0.5(H₂O)]_n (Tb-DTA) (H₂DTA = 2,5-di(1H-imidazol-1-yl)terephthalic acid), are successfully synthesized via a hydrothermal reaction. Single-crystal X-ray diffraction analyses demonstrate that the extended π conjugated ligand plays an important role in the coordination mode and topologies. Eu-DTA possesses a 4,6-connected three-dimensional topological structure, while Tb-DTA exhibits a 4,5-connected three-dimensional framework. Interestingly, the rich uncoordinated nitrogen or oxygen atoms in these two structures can be used as Lewis basic sites, showing strong sensitivity to metal ions and solvent molecules. Furthermore, luminescence and sensing studies reveal that Eu-DTA and Tb-DTA can sensitively and simultaneously detect Fe³⁺ ions and nitrobenzene, which suggests that the two Ln-MOFs are promising bifunctional luminescence sensors. The quenching mechanism for Fe³⁺ has been discussed in detail.