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

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 Ln(2)(H2O)(4)(pzdc)(3)center dot(3/3.5)H2O with Ln = Pr (1), Nd (2), Sm (3), Eu (4) is built up from dinuclear bricks [Ln(2)O(8)N(5)(H2O)(4)] containing two mu(3)-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-Ln(2)O(8)N(5)(H2O)(4) networks, intercalated by free water molecules. The second series with chemical formula Ln(2)(H2O)(6)(pzdc)(3)center dot 3H(2)O (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 [Ln(2)O(6)N(5)(H2O)(6)]. Interactions via hydrogen 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.