Crystal Structure, Multiplex Photoluminescence, and Magnetic Properties of a Series of Lanthanide Coordination Polymers Based on Quinoline Carboxylate Ligand

A series of novel one-dimensional (1D) lanthanide coordination polymers, [Ln­(pqc)­(Hpqc)­(NO₃)₂]_n (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), Tm (8), Yb (9), or Lu (10); Hpqc = 2-phenyl-4-quinolinecarboxylic acid), have been synthesized via solvothermal reaction at low temperature and then characterized by single-crystal X-ray diffraction. Polymers 1–10 are isostructural and feature a 1D chain based on binuclear units in which Ln³⁺ polyhedra are interconnected by bridging Hpqc ligands and terminal nitrates. The infinite chains are further extended to a three-dimensional supramolecular framework through π···π stacking and hydrogen bonding interactions. This series affords an opportunity to study the lanthanide contraction effect, demonstrating that the sum of Ln–O distances proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. The photoluminescence spectra show that these complexes are highly sensitized by Hpqc and exhibit characteristic Ln³⁺ (Sm (1), Eu (2), Tb (4), Er (7), and Yb (9)) and ligand centered (Dy (5), Ho (6), Tm (8), and Lu (10)) luminescence in both visible and near-infrared (NIR) regions. The magnetic properties of 4–7 have also been investigated.