title: Stoichiometry and structure of uranylVI hydroxo dimer and trimer complexes in aqueous solution.
abstract: We studied the structure and stoichiometry of aqueous uranylVI hydroxo dimers and trimers by spectroscopic (EXAFS, FTIR, UV-vis) and quantum chemical (DFT) methods. FTIR and UV-vis spectroscopy were used for the speciation of uranyl complexes in aqueous solution. DFT calculations show that (UO2)2(OH)22+ has two bridging hydroxo groups with a U-U distance of 3.875 A. This result is in good agreement with EXAFS, where a U-U distance of 3.88 A was found. For the hydroxo trimer complex, DFT calculations show that the species (UO2)3(O)(OH)3+ with oxo bridging in the center is energetically favored in comparison to its stoichiometric equivalent (UO2)3(OH)5+. This is again in line with the EXAFS result, where a shorter U-U distance of 3.81-3.82 A and evidence for oxo bridging in the center were found. Several stable intermediates which lie several tens of kJ/mol above that of (UO2)3(O)(OH)3+ were identified, and their structures, energies, and intramolecular proton-transfer reaction are discussed.
authors.affiliation: Institut für Radiochemie, Forschungszentrum Dresden-Rossendorf (FZD), Bautzner Landstrasse 128, D-01328, Dresden, Germany. S.Tsushima@fzd.de
authors.forename: Satoru
authors.initials: S
authors.lastname: Tsushima
authors.forename: André
authors.initials: A
authors.lastname: Rossberg
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ikeda
authors.forename: Katharina
authors.initials: K
authors.lastname: Müller
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost