Layer-structured lanthanide coordination polymers constructed from 3,5-bis(3,5-dicarboxylphenyl)-pyridine ligand as fluorescent probe for nitroaromatics and metal ions

A series of lanthanide coordination polymers (Ln-CPs) {(Me₂NH₂⁺)[Ln(L)(H₂O)₂]}_n (1–5) [Ln = Eu(1), Tb(2), Gd(3), Sm(4) and Pr(5)], were synthesized through the self-assembly of symmetric tetracarboxylic acid 3,5-bis(3,5-dicarboxylphenyl)-pyridine (H₄L) and different lanthanide ions. Ln-CPs 1–5 are isostructural and show two-dimensional (2D) layered structure constructed from LnO₉ tricapped trigonal prisms and L⁴⁻ ligands. Solid state luminescent studies illustrate that 1, 2 and 4 exhibit the characteristic emission of the corresponding Ln³⁺ ions, while 3 reveals blue emission arising from the organic ligand and 5 shows characteristic luminescence emission bands of Pr³⁺ ions in the near-infrared region (NIR). Notably, 1 exhibits good luminescent sensing for metal ions, such as Cr₂O₇²⁻ ions, MnO₄⁻ ions, Fe³⁺ ions, and small organic molecules, including acetone and trinitrophenol (TNP).