Triazole-Based Cu(I) Cationic Metal–Organic Frameworks with Lewis Basic Pyridine Sites for Selective Detection of Ce3+ Ions

A highly symmetric bis-triazole-pyridine-based organic ligand, i.e., 3,5-di(4H-1,2,4-triazol-4-yl)pyridine (L), and Cu(II) salts were used to synthesize three cationic Cu(I) metal-organic frameworks (MOFs), namely, {[Cu(L)]·(NO₃)·(H₂O)}_n (1), {[Cu(L)]·(BF₄)·0.5H₂O}_n (2), and {[Cu_1.25(L)]·1.25(ClO₄)·H₂O}_n (3). All three MOFs have nonbonded anions situated inside the pore spaces. Both 1 and 2 have a two-dimensional network structure, while 3 has a three-dimensional structure. All three MOFs were characterized using Fourier transform infrared spectroscopy, elemental (C, H, and N) analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. Due to the presence of a Lewis basic pyridine moiety, these MOFs could serve as luminescent probes for the selective detection of Ce³⁺ ions with excellent efficiency (10^-7 M). The synthesis of Cu(I)-based MOFs and their use to detect Ce³⁺ ions in water via a turn-on fluorescence process have rarely been reported. These MOFs are highly stable in water, are recyclable, and function efficiently at different pH values.