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

Abstract

New lanthanide complexes of 2-hydroxynicotinic acid (H 2nicO) [Ln(HnicO) 2(μ-HnicO)(H 2O)] · nH 2O (Ln=Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb(HnicO) 2(μ-HnicO)(H 2O)] · 1.75H 2O ( 1) and [Eu(HnicO) 2(μ-HnicO)(H 2O)] · 1.25H 2O ( 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 Eu 3+ and Tb 3+ emitting states, 5D 0 and 5D 4, respectively. A value around 30% was found for the 5D 0 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 Gd 3+-based complexes.