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Title: Pentavalent neptunyl ([OΞNpΞO] +) cation–cation interactions in aqueous/polar organic mixed-solvent media

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O] +) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalent linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al 3+, Sc 3+, Cr 3+, Fe 3+, In 3+ and UO 2+ 2) and the pentavalent neptunyl cation (NpO + 2, whose coordination chemistry is similar tomore » that of AmO + 2 while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. As a result, the Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the NpO + 2 • Cr 3+ complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.« less
 [1] ;  [2] ;  [1]
  1. Washington State Univ., Pullman, WA (United States)
  2. Idaho National Lab. (INL), Idaho Falls, ID (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Solution Chemistry
Additional Journal Information:
Journal Volume: 46; Journal Issue: 6; Journal ID: ISSN 0095-9782
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; cation–cation interactions; neptunyl; mixed-solvents
OSTI Identifier: