The Syntheses, Structures, and Selective Detection Properties for Fe³⁺, MnO₄^–, Cr₂O₇^2–, and Nitroaniline of Two Multifunctional Lanthanide Coordination Polymers

Two novel lanthanide coordination polymers (CPs), [Ln2(CPPCA)3(H2O)3]n (Ln = Eu Eu-CPPCA, Ln = Tb Tb-CPPCA, H2CPPCA = 1-(4-carboxy-phenyl)-piperidine-4-carboxylic acid), were produced via the solvothermal process and characterized by various means, including elemental analysis (EA), Fourier transform Infrared spectra (FT-IR), single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), and thermal gravimetric analysis (TGA). Based on the {Eu2(COO)6} binuclear units, both compounds present a 5-nodal 3D network with a topology symbol of {4.62}2{42.62.86.105}{42.64.814.106.122}{4}2{6}2. Eu-CPPCA displays the emission bands from the ligand (π* → π), while Tb-CPPCA exhibits the intrinsic typical emission peak of Tb3+ (5D4 → 7FJ). The fluorescence performance studies show that Eu-CPPCA and Tb-CPPCA can detect Fe3+ (Ksv = 4.21 × 104 M–1, LOD = 0.403 μM), MnO4– (Ksv = 3.72 × 104 M–1, LOD = 0.460 μM), Cr2O72– (Ksv = 2.06 × 104 M–1, LOD = 0.826 μM), o-nitroaniline (o-NA, Ksv = 3.28 × 104 M–1, LOD = 0.520 μM), and Fe3+ (Ksv = 1.74 × 105 M–1, LOD = 0.0466 μM), MnO4– (Ksv = 8.62 × 104 M–1, LOD = 0.0941 μM), p-nitroaniline (p-NA, Ksv = 8.66 × 104 M–1, LOD = 0.0936 μM), with high sensitivity, good reproducibility, and lower detection limits, indicating that both two compounds might be potential fluorescence sensors. Discussions were also conducted regarding the potential sensing mechanism.