We used pentacarboxylic acid ligand 3, 5-di(2', 4'-dicarboxylphenyl) benzoic acid (H₅L) to synthesize two structural similarity lanthanide-cobalt heteronuclear bimetallic organic frameworks (Ln-Co-MOFs) by hydrothermal method: (C₂H₆NH₂)₅{[Eu₉Co(L)₆(H₂O)₅(OH)₄] ·5DMF}_n (1), (C₂H₆NH₂)₂{[Sm₉Co(L)₆(H₂O)₃Cl] ·5DMF}_n (2). The structures were characterized and the property was tested by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetry, infrared, fluorescence spectra, and magnetism. The results show that 1 and 2 both belong to the trigonal R3 space group and have novel 3D structures and good thermal stability. Among them, 1 has strong fluorescence properties, which can sensitively identify drug molecules sulfasalazine and organic molecules glutaraldehyde. The detection limits could reach 0.95 and 2.10 μmol·L^-1, respectively. In addition, 1 and 2 were antiferromagnetic at 1 kOe.

In this study, using 3, 5-di(3′, 5′-dicarboxylphenyl)-1H-1, 2, 4-triazole (H₄L) as ligands, a gadolinia-based organic framework complex {[GdNa(L)(H₂O)₃]·2H₂O}_n (Gd-Na-MOF) was successfully designed and synthesized by hydrothermal method. The structure and properties were systematically characterized and tested by techniques such as single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and fluorescence spectroscopy. The results indicate that this complex has a unique 3D structure, excellent thermal stability, and outstanding luminescent performance. Based on its luminescent properties, a polymer-embedding method was employed to fabricate the Gd-Na-MOF into a flexible, washable composite fluorescent film, Gd-Na-MOF@PMMA/BMA (PMMA=polymethyl methacrylate, BMA=butyl methacrylate). This fluorescent film exhibited highly sensitive recognition capability for tyramine, with a low detection limit of 1.66 μmol·L^-1. It was used for the detection of tyramine in bananas, with a recovery rate of 96.92%-100.26%.

To address the challenges of poor solubility and difficult recyclability of powdered metal-organic frameworks (MOFs), a Eu-based MOF complex, [EuNa(L)(H₂O)₃]·2H₂O (Eu/Na-MOF), was synthesized by the hydrothermal method using 3,5-bis(3,5-dicarboxyphenyl)-1H-1,2,4-triazole (H₄L) as the ligand in this study. Systematic characterization and performance evaluation revealed that the complex exhibits a unique 3D structure, high phase purity, excellent thermal stability, and outstanding luminescent properties. Furthermore, the complex was encapsulated in poly(methyl methacrylate) (PMMA) to fabricate a flexible and water-washable composite fluorescent film (Eu/Na-MOF/PMMA). Based on static and dynamic quenching mechanisms, respectively, the film enables reversible detection of tryptamine and Cr₂O₇^2- ions in aqueous solutions, demonstrating high selectivity, stability, and portability.