Lanthanide–organic framework based on a 4,4-(9,9-dimethyl-9H-fluorene-2,7-diyl) dibenzoic acid: Synthesis, structure and fluorescent sensing for a variety of cations and anions simultaneously

Based on the structural diversity and the superior luminescence properties of 4,4-(9,9-dimethyl-9H-fluorene-2,7-diyl) dibenzoic acid (H2DLDA), a series of new lanthanide coordination compounds [Ln(DLDA)(DMF)(H2O)(COO)]n (Sm (1), Eu (2), Ce (3), Nd (4), Gd (5)) were successfully prepared by the reaction of H2DLDA, which is a new type ligand synthesized by structural modification of fluorene, with rare earth metal ion. They were characterized by elemental analysis, IR, TG, PXRD, UV–vis, etc. Analysis results show that the coordination compounds are isomorphic. In particular, the structure of the coordination compound 1 was determined by single crystal X-ray diffraction. The structure analysis shows that compound 1 is a novel 3D supramolecular network structure, and the central metal adopts the eight-coordination mode to form a double-cap triangular prism spatial configuration. It is worth mentioning that the excellent heat-resisting ability of the framework, which is stable until heated to nearly 400 °C. Meanwhile, the fluorescence sensing test showed that as synthesized compound 2 was a new type of fluorescent probe with high efficiency, high selectivity and has the ability to simultaneously detect a variety of cations and anions (Fe3+, Al3+, Cr3+, C2O42−, Cr2O72−, MnO4−, PO43−). Moreover, it owns higher Ksv value (1.77 × 104 M−1, 1.44 × 104 M−1, 3.621 × 104 M−1, 2.07 × 103 M−1, 5.65 × 103 M−1, 3.18 × 103 M−1, 1.82 × 103 M−1, respectively) and a lower detection limit (1.93 μM, 2.38 μM, 0.945 μM, 16.5 μM, 6.06 μM, 10.8 μM, 18.8 μM, respectively). This results in compound 2 being superior to other probes reported previously, and the mechanism of fluorescence quenching was explained to some extent. In addition, during the fluorescence titration experiment, we found an interesting luminescence change of compound 2. Most notably, it emitted white light in DMA solvent under the irradiation of handheld ultraviolet lamp (wavelength: 365 nm) while the solid sample emitted yellow light at the same conditions.