Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: a new luminescent uranyl benzoate specie.
Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3](-) which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68μs which is much more compared to the lifetime of uncomplexed uranyl (20μs) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3](-) specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.
Luminescence of uranyl ion complexed with 2,6-pyridine dicarboxylic acid as ligand in acetonitrile medium: observation of co-luminescence
Abstract Luminescence from UO22+ (uranyl ion) complexed with 2,6-pyridine dicarboxylic acid (PDA) has been studied using acetonitrile (MeCN) as solvent between pH 1.0 and 6.0. The enhancement in luminescence intensity because of sensitization by PDA in the non-aqueous environment provided by the MeCN is found to be one order better than in aqueous medium. The luminescence is further enhanced by about four times following the addition of Y3+; a process known as co-luminescence. This is the first study on co-luminescence of uranyl ion in its PDA complex. Lifetime studies indicate the presence of two species having different micro-environments. Formations of both intra and inter molecular complexes are believed to be responsible for enhancement due to co-luminescence.
Lanthanide complexes of 2-hydroxynicotinic acid: synthesis, luminescence properties and the crystal structures of [Ln(HnicO)2(μ-HnicO)(H2O)] · nH2O (Ln=Tb, Eu)
Abstract New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO) [Ln(HnicO)2(μ-HnicO)(H2O)] · nH2O (Ln=Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb(HnicO)2(μ-HnicO)(H2O)] · 1.75H2O (1) and [Eu(HnicO)2(μ-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 Eu3+ and Tb3+ 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 Gd3+-based complexes.