First Identification and Thermodynamic Characterization of the Ternary U(VI) Species, UO2(O2)(CO3)24−, in UO2−H2O2−K2CO3 Solutions

George S. Goff†, Lia F. Brodnax†, Michael R. Cisneros†, Shane M. Peper‡, Stephanie E. Field†, Brian L. Scott§ and Wolfgang H. Runde*†
Chemistry and Material Physics and Applications Divisions, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, Chemical and Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, and Material Physics and Applications Divisions, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Inorg. Chem., 2008, 47 (6), pp 1984–1990
DOI: 10.1021/ic701775g
Publication Date (Web): February 22, 2008
Copyright © 2008 American Chemical Society
†

Chemistry and Material Physics and Applications Divisions, Los Alamos National Laboratory.

,
‡

Chemical and Physical Sciences Division, Pacific Northwest National Laboratory.

,
§

Material Physics and Applications Divisions, Los Alamos National Laboratory.

,
* To whom correspondence should be addressed. E-mail: runde@lanl.gov.

Abstract

Abstract Image

In alkaline carbonate solutions, hydrogen peroxide can selectively replace one of the carbonate ligands in UO2(CO3)34- to form the ternary mixed U(VI) peroxo-carbonato species UO2(O2)(CO3)24−. Orange rectangular plates of K4[UO2(CO3)2(O2)]·H2O were isolated and characterized by single crystal X-ray diffraction studies. Crystallographic data: monoclinic, space group P21/n, a = 6.9670(14) Å, b = 9.2158(10) Å, c = 18.052(4) Å, Z = 4. Spectrophotometric titrations with H2O2 were performed in 0.5 M K2CO3, with UO2(O2)(CO3)24− concentrations ranging from 0.1 to 0.55 mM. The molar absorptivities (M−1 cm−1) for UO2(CO3)34− and UO2(O2)(CO3)24− were determined to be 23.3 ± 0.3 at 448.5 nm and 1022.7 ± 19.0 at 347.5 nm, respectively. Stoichiometric analyses coupled with spectroscopic comparisons between solution and solid state indicate that the stable solution species is UO2(O2)(CO3)24−, which has an apparent formation constant of log K′ = 4.70 ± 0.02 relative to the tris-carbonato complex.

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History

  • Published In Issue March 17, 2008
  • Article ASAPFebruary 22, 2008
  • Received: September 10, 2007

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