Interaction of 3-Hydroxypicolinamide with TbIII and its Sensitizing Effect on Terbium Luminescence as a Function of pH and Medium
Abstract
Coordination behaviour of 3-hydroxypicolinamide (HPA) towards TbIII is studied in aqueous and micellar media. The complex formed exists asML2 species in which HPA behaves as anO,O,N,N-chelating ligand. The solid complex is isolated from aqueous medium and characterized employing elemental analysis, TG/DTA, magnetic, IR, ESR and mass spectral data. Stability constant and other accompanying thermodynamic parameters of the TbIII complex have been determined pHmetrically. The complexation reaction is spontaneous and exothermic. Effect of micelles andpHon the luminescence of TbIII were also studied. The emission peaks of TbIII are highly sensitized on complexation with HPA and the optimum luminescence efficiency is obtained in slightly acidic to neutral solutions (pH 6–8). The complex decays biexponentially and the presence of ethanol and surfactants causes a large increase in the luminescence intensity protecting the complex fromradiationless deactivation processes.
KEYWORDS: 3-Hydroxypicolinamide, stability constant, micelles, terbium luminescence, sensitization.
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