Speciation and Coordination Chemistry of Uranyl(VI)-Citrate Complexes in Aqueous Solution

Sofie P. Pasilis, Jeanne E. Pemberton

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The pH dependence of uranyl(VI) complexation by citric acid was investigated using Raman and attenuated total reflection FTIR spectroscopies and electrospray ionization mass spectrometry. pH-dependent changes in the νs(UO2) envelope indicate that three major UO 22+-citrate complexes with progressively increasing U=O bond lengths are present over a range of pH from 2.0 to 9.5. The first species, which is the predominant form of uranyl(VI) from pH 3.0 to 5.0, contains two UO22+ groups in spectroscopically equivalent coordination environments and corresponds to the [(UO2)2Cit 2]2- complex known to exist in this pH range. At pH values >6.5, [(UO2)2Cit2]2- undergoes ah an interconversion to form [(UO2)3Cit 3]3- and (UO2)3Cit2. ESI-MS studies on solutions of varying uranyl(VI)/citrate ratios, pH, and solution counteranion were successfully used to confirm complex stoichiometries. Uranyl and citrate concentrations investigated ranged from 0.50 to 50 mM.

Original languageEnglish (US)
Pages (from-to)6793-6800
Number of pages8
JournalInorganic Chemistry
Issue number21
StatePublished - Oct 20 2003


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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