Lanthanide complexes of 2-hydroxynicotinic acid: synthesis, luminescence properties and the crystal structures of [Ln(HnicO)(2)(mu-HnicO)(H(2)O)] .nH(2)O (Ln = Tb, Eu)

Abstract

New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO) [Ln(HnicO)2(l-HnicO)(H2O)] nH2O (Ln¼Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb(HnicO)2(l-HnicO)(H2O)] 1.75H2O (1) and [Eu(HnicO)2(l-HnicO)(H2O)] 1.25H2O (2) complexes were determined by X-ray diffraction. The 2-hydroxynicotinate ligand coordinates through O,O-chelation to the lanthanide(III) ions as shown by X-ray diffraction and the infrared, Raman and NMR spectroscopy results. Photoluminescence measurements were performed for the Eu(III) and Tb(III) complexes. Lifetimes of 0.592 0.007 and 0.113 0.002 ms were determined for the Eu3þ and Tb3þ emitting states, 5D0 and 5D4, respectively. A value around 30% was found for the 5D0 quantum efficiency. The energy transfer mechanisms between the lanthanide ions and the ligands are discussed and compared with those observed in similar complexes involving the 3-hydroxypicolinate ligand based on the luminescence of the respective Gd3þ-based complexes.