Lanthanide-based 0D and 2D molecular assemblies with the pyridazine-3,6-dicarboxylate linker

Abstract

Two distinct series of lanthanides-based coordination polymers involving the pyridazine-3,6-dicarboxylate (pzdc) ligand have been structurally characterized by means of single-crystal XRD analysis. The structure of the compounds Ln₂(H₂O)₄(pzdc)₃·(3/3.5)H₂O with Ln = Pr (1), Nd (2), Sm (3), Eu (4) is built up from dinuclear bricks [Ln₂O₈N₅(H₂O)₄] containing two μ₃-oxo bridged nine-fold coordinated lanthanide cations, connected via the pzdc ligand, which acts as tetratendate, tridentate or monodentate linkers. It results in the generation of layers of mixed pzdc-Ln₂O₈N₅(H₂O)₄ networks, intercalated by free water molecules. The second series with chemical formula Ln₂(H₂O)₆(pzdc)₃·3H₂O (Ln = Gd (5), Tb (6), Dy (7), Er (8), Lu (9)) is a molecular assembly of discrete dinuclear bricks similar to those of the previous compounds. They only differ by the number of terminal water molecules within the dimer [Ln₂O₆N₅(H₂O)₆]. Interactions viahydrogen bond occur between terminal water species attached the lanthanide and free intercalated water molecules. Europium- and terbium-based compounds 4 and 6 exhibit fluorescence emission in the visible region at room temperature.