Polynuclear complexes constructed by lanthanides and pyridine-3,5-dicarboxylate ligand: Structures, thermal and luminescent properties

Sodium salt of pyridine-3,5-dicarboxylic acid (H2pdc) reacts with the chloride (or nitrate) salt of lanthanides(III) (from La to Lu, except Pm) under hydrothermal conditions to form different kinds of coordination frameworks. The compounds of the general formula Ln2pdc3·nH2O (pdc2− = C5H3N(COO)22−, n = 2.64–14) are characterized in the solid state by elemental analysis, IR spectroscopy, TG-DSC and TG-FTIR analyses, single-crystal X-ray diffraction, and X-ray powder diffraction (XRPD) techniques as well as fluorescent spectroscopy. The crystalline compounds form isostructural groups: Sm-Gd, Tb-Er and Tm-Lu. The crystal structures of [Ho2pdc3(H2O)2]·0.64H2O (1), [Er2pdc3(H2O)2]·0.68H2O (2) and [Yb4pdc6(H2O)18]·10H2O (3) compounds are reported. The compounds 1 and 2 are built up from metallic centrosymmetric dimers connected by pdc2− ligands into the 3D frameworks. There are observed 1D channels occupied by water molecules. In compound 3, the four Yb(III) centers are bridged through pdc2− ligands into the cyclic tetranuclear structure. These molecules are further assembled into a 3D supramolecular framework. This appears to be a rare example of cyclic polynuclear compounds generated by lanthanide(III) ions and polycarboxylate ligands. The luminescent properties of the complexes in visible and infrared regions upon UV excitation are discussed.

Graphical abstractThe series of lanthanide(III) pyridine-3,5-dicarboxylates was synthesized and characterized. The compounds are isostructural in groups: Sm-Gd, Tb-Er and Tm-Lu. The crystal structures of 3D coordination polymers of Ho and Er as well as cyclic tetramer of Yb were described. The luminescent properties of the compounds in Vis and NIR regions were discussed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The series of lanthanide(III) pyridine-3,5-dicarboxylates was synthesized under hydrothermal conditions. ► Their thermal and luminescence properties have been investigated. ► The crystal structures of 3D coordination polymers of Ho and Er as well as cyclic tetramer of Yb were described.