Visible and NIR Photoluminescence Properties of a Series of Novel Lanthanide-Organic Coordination Polymers Based on Hydroxyquinoline-Carboxylate Ligands

A series of novel two-dimensional (2D) lanthanide coordination polymers with 4-hydroxyquinoline-2-carboxylate (H(2)hqc) ligands, [Ln(Hhqc)(3)(H2O)](n)center dot 3nH(2)O (Ln = Eu (1), Tb (2), Sm (3), Nd (4), and Gd (5)) and [Ln(Hhqc)(ox)(H2O)(2)](n) (Ln = Eu (6), Tb (7), sm (8), Tm (9), Dy (10), Nd (11), Yb (12), and Gd (13); H(2)ox = oxalic acid), have been synthesized under hydrothermal conditions. Complexes 1-5 are isomorphous, which can be described as a two-dimensional (2D) hxl/Shubnikov network based on Ln(2)(CO2)(4) paddle-wheel units, and the isomorphous complexes 6-13 feature a 2D decker layer architecture constructed by Ln-ox infinite chains cross-linked alternatively by bridging Hhqc(-) ligands. The room-temperature photoluminescence spectra of complexes Eu-III (1 and 6), Tb-III (2 and 7), and Sm-III (3 and 8) exhibit strong characteristic emissions in the visible region, whereas Nd-III (4 and 11) and Yb-III (12) complexes display NIR luminescence upon irradiation at the ligand band. Moreover, the triplet state of H2hqc matches well with the emission level of Eu-III, Tb-III and Sm-III ions, which allows the preparation of new optical materials with enhanced luminescence properties.