Synthesis, structure and properties of 2D lanthanide coordination polymers based on N-heterocyclic arylpolycarboxylate ligands

Abstract

The reaction of 3-(2,4-dicarboxyphenyl)-2,6-pyridinedicarboxylic acid (H₄dppd) with rare earth nitrates under hydrothermal conditions generated a series of new two-dimensional (2D) coordination polymers, namely {[La(Hdppd)(H₂O)₂·(H₂O)₂]_n (1), [Ln₂(Hdppd)₂(H₂O)₄·(H₂O)₃]_n [Ln = Sm (2), Eu (3)] and [Ln(Hdppd)(H₂O)₃·H₂O]_n [Ln = Gd (4), Tb (5), Dy (6), Ho (7), Er (8)] [Hdppd = 3-(2,4-dicarboxyphenyl)-2,6-pyridinedicarboxylic trivalent anion]}. The complexes were characterized by X-ray single-crystal diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. Luminescence spectroscopy of 3 and 5 showed bright red and green luminescences due to the 4fⁿ–4fⁿ transitions in Eu³⁺ and Tb³⁺ respectively, although the luminescence lifetime is shortened by non-radiative decay due to the presence of coordinating water molecules. The magnetic properties of 2–8 were measured and discussed. Compound 6 exhibits frequency dependent out-of-phase signals, and ferromagnetic coupling exists in 8.