title: Stoichiometry, stability constants and coordination geometry of Eu(III) 5-sulfosalicylate complex in aqueous system-A TRLIFS study.
abstract: The complex formation between Eu(III) and 5-sulfosalicylate, (HSSA)(2-), has been investigated by means of TRLIFS (time resolved laser induced fluorescence spectroscopy). The concentration of free ligand in the solution was determined from the fluorescence emission of 5-sulfosalicylate by subtracting the dynamic quenching effect from the observed quenching of fluorescence emission by means of lifetime analysis, and the stoichiometry and the corresponding formation constants were obtained. A carboxylate coordinated complex, Eu(HSSA)(+), and also a chelate complex, Eu(SSA), were identified, and the formation constants of the complex Eu(HSSA)(2+) for the reaction, Eu(3+)+ HSSA(2-)[rightward arrow] Eu(HSSA)(+), and the deprotonation constant of the chelating reaction, Eu(HSSA)(+)--> Eu(SSA)+ H(+), were calculated at log beta(1,1)= 1.79 and log K'=-5.78, respectively. TRLIFS using the fluorescence emission from Eu(III) was performed in order to determine the number of coordination waters of the complex Eu(HSSA)(2+). The quenching of the Eu(III) fluorescence caused by (SSA)(3-) disturbed the lifetime analysis of the 'intrinsic lifetime' of Eu(III) in Eu(HSSA)(2+), however the problem was successfully solved by the analysis of emission intensity and lifetime, and the formulation of the complex was determined as [Eu(HSSA)8H(2)O](2+) with the explicit involvement of the coordinated waters.
authors.affiliation: Department of Quantum Engineering and Systems Science, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656, Tokyo, Japan. tora@flanker.q.t.u-tokyo.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Toraishi
authors.forename: Noboru
authors.initials: N
authors.lastname: Aoyagi
authors.forename: Shinya
authors.initials: S
authors.lastname: Nagasaki
authors.forename: Satoru
authors.initials: S
authors.lastname: Tanaka