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 (H2hqc)
ligands, [Ln­(Hhqc)3(H2O)]n·3nH2O (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); H2ox = 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 Ln2(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 EuIII (1 and 6),
TbIII (2 and 7), and SmIII (3 and 8) exhibit strong characteristic
emissions in the visible region, whereas NdIII (4 and 11) and YbIII (12) complexes
display NIR luminescence upon irradiation at the ligand band. Moreover,
the triplet state of H2hqc matches well with the emission
level of EuIII, TbIII, and SmIII ions,
which allows the preparation of new optical materials with enhanced
luminescence properties.