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Report No.

Luminescence and potentiometric studies on the complexation of europium(III) by picolinate in an aqueous solution

Aoyagi, Noboru; Toraishi, Takashi*; Nagasaki, Shinya*; Tanaka, Satoru*

The complexation behavior of Eu$$^{3+}$$ aquo ions by picolinic acid in aqueous solutions is investigated so as to describe the formation of poly nuclear complexes which are uncommon for trivalent lanthanides. Potentiometric titration exhibited that no poly-nuclear complexes form via hydroxide bridges even at high pH, providing a monomeric form, [Eu(Pic)$$_{4}$$$$cdot$$(H$$_{2}$$O)]$$^{-}$$, with picolinate ligand in a large excess. In addition, the lifetime analysis of Eu$$^{3+}$$ luminescence in time-resolved laser-induced fluorescence spectroscopy was performed under the condition where Eu(pic)$$^{2+}$$ appears as the secondary dominant species. The result showed the strong quenching of luminescence, suggesting the polymeric complexes, [Eu(Pic)]$$_{m}$$$$^{2m+}$$, form even at low pH due to the vicinal Eu-Eu interaction.



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