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Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO4-

  • Author(s): De Jong, WA
  • Dau, PD
  • Wilson, RE
  • Marçalo, J
  • Van Stipdonk, MJ
  • Corcovilos, TA
  • Berden, G
  • Martens, J
  • Oomens, J
  • Gibson, JK
  • et al.
Abstract

© 2017 American Chemical Society. The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)−, where An = Pa or U, are essentially actinyl ions, AnVO2+, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO(OH)2(C2O4)−. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVIis inaccessible, UVIis very stable. The UVO2(C2O4)−complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2to yield UO4-and two CO2molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO22+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of −1.5 and U-O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)−toward O2is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4-, reacts with water to yield UO5H2-. Infrared spectra obtained for UO5H2-confirm the computed lowest-energy structure, UO3(OH)2-

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