Syntheses, structures and luminescence properties of five lanthanide–isonicotinate coordination polymers

Five isostructural compounds of lanthanide with isonicotinate ligand, formula as [Ln(IN)2(H2O)4](NO3) (Ln = La, Nd, Eu, Tb and Er, 1−5, IN = isonicotinate), were synthesized under hydrothermal conditions by tuning the pH level and the ratio of lanthanide with isonicotinic acid. These compounds were characterized by single-crystal X-ray structure analysis, elemental analysis, IR and TG-DTA. In five compounds, the adjacent eight-coordination lanthanide centers were linked together through the bidentate bridging carboxylate groups of isonicotinate ligands to generate infinite chain structures which were further interconnected to form 3D supramolecular networks via the OW–H···N (nitrogen atom came from isonicotinate ligands) and OW–H···O (oxygen atom came from nitrate) hydrogen bonds. Compounds 3 and 4 show strong red and green emission, corresponds to 5D0→7F2 transition of Eu3+ ions and 5D4→7F5 transition of Tb3+ ions, respectively.