title: Ternary complex formation of Eu(III) with o-phthalate in aqueous solutions.
abstract: Ternary hydroxo complex formation of Eu(III) with o-phthalate was investigated by potentiometry and fluorescence spectrophotometry. Curves of the equilibrium pH versus the amount of NaOH added showed that the pH value starting to form a Eu(III) precipitate was decreased due to the formation of a ternary hydroxo complex, EuOHL(s) (L = phthalate). The formation of EuOHL(s) was qualitatively confirmed by the enhancement of the fluorescence intensity of Eu(III) in the precipitate with the light absorbed by phthalate, and was quantitatively confirmed by the measurement of the amounts of Eu(III), OH(-) and phthalate included in the precipitate. The solubility product of EuOHL(s) was determined as pK(sp)(0) = 15.6+/-0.4. Characteristic features in the fluorescence spectra and the solubility product of the Eu(III)-phthalate complex were compared with those of the Eu(III)-PDA (PDA = pyridine-2,6-dicarboxylate) complex. The fluorescence intensity of the EuL(+) complex of L = PDA was about 11 times stronger than that of L = phthalate. The origin of the difference in the fluorescence intensity is discussed based on the intramolecular energy transfer effect from the lowest triplet energy level of the ligand to the resonance energy level of Eu(III).
authors.affiliation: Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, P.O. Box 105, Yuseong, Daejeon 305-600, Republic of Korea. nkkpark@kaeri.re.kr
authors.forename: K K
authors.initials: KK
authors.lastname: Park
authors.forename: E C
authors.initials: EC
authors.lastname: Jung
authors.forename: H-R
authors.initials: HR
authors.lastname: Cho
authors.forename: W H
authors.initials: WH
authors.lastname: Kim
mesh_terms: D005063:Europium / Q000737:chemistry*; D008024:Ligands; D010795:Phthalic Acids / Q000737:chemistry*; D010848:Picolinic Acids / Q000737:chemistry*; D011199:Potentiometry; D012995:Solubility; D013053:Spectrophotometry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D008024:Ligands; D010795:Phthalic Acids; D010848:Picolinic Acids; D014867:Water; D005063:Europium; C032279:phthalic acid; C004860:dipicolinic acid