title: Comparative EXAFS investigation of uranium(VI) and -(IV) aquo chloro complexes in solution using a newly developed spectroelectrochemical cell.
abstract: The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U L(III)-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gastight spectroelectrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)5(2+), UO2(H2O)4Cl+, UO2(H2O)3Cl2(0), and UO2(H2O)2Cl3- with [Cl-] increasing from 0 to 9 M, and for U(IV) we observed the complexes U(H2O)9(4+), U(H2O)8Cl3+, U(H2O)(6-7)Cl2(2+), and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.76+/-0.02 A, Oeq = 2.41 +/- 0.02 A, and U-Cl = 2.71 +/- 0.02 A; the distances in the U(IV) coordination sphere are U-O = 2.41 +/- 0.02 A and U-Cl = 2.71 +/- 0.02 A.
authors.affiliation: Forschungszentrum Rossendorf, Institute of Radiochemistry, P.O. Box 510119, 01314 Dresden, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hennig
authors.forename: J
authors.initials: J
authors.lastname: Tutschku
authors.forename: A
authors.initials: A
authors.lastname: Rossberg
authors.forename: G
authors.initials: G
authors.lastname: Bernhard
authors.forename: A C
authors.initials: AC
authors.lastname: Scheinost