Journal article
Sensitivity of Solvation Environment to Oxidation State and Position in the Early Actinide Period
Inorganic chemistry, Vol.54(13), pp.6216-6225
07/06/2015
Handle:
https://hdl.handle.net/2376/108504
PMID: 26091144
Abstract
The aqueous solvation of U-Pu in the III-VI oxidation states has been examined using density functional theory and hydrated cluster models of the form An(H2O)30(4+/3+) and AnO2(H2O)30(2+/+) embedded within a polarizable continuum model to approximate the effect of bulk water. The structural features are compared to available data from extended X-ray absorption fine structure. Then, using a multiple-scattering approach, the X-ray absorption near-edge spectra (XANES) have been simulated and compared to experiment. These structural data are complemented by a detailed thermodynamic analysis using a recently benchmarked protocol. The structural, spectroscopic, and thermodynamic information has been used to assign the primary solvation environments in water, with an emphasis upon understanding how oxidation state and position in the period modifies the hydration number and equilibrium between different solvation shell environments. Tetravalent U is proposed to exist in equilibrium between the 8- and 9-coordinate species. Moving to the right of the period, Np(IV) and Pu(IV) exist solely as the octa-aquo species. Reduction to the trivalent ions leads to thermodynamic favorability for this solvation environment, whose features reproduce the XANES spectra. The actinyl dications (AnO2(2+)) of U and Np have a preferred environment in the equatorial plane consisting of 5 solvating waters; however, changes to the ionic radius and electronic structure at Pu leads to an equilibrium between the 4- and 5-coordinate species for PuO2(2+). Reduction of the dications to form the monocations generally leads to a preference for the 4-coordinate primary solvation shell, with an equilibrium existing for uranyl, while the neptunyl and plutonyl species exist solely as AnO2(H2O)4(+). These data provide accurate thermodynamic information for several rare species and the combined thermodynamic, structural, and spectroscopic approach reveals trends in hydration behavior across actinide oxidation states and within the early actinide period.
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Details
- Title
- Sensitivity of Solvation Environment to Oxidation State and Position in the Early Actinide Period
- Creators
- Aurora E Clark - †Department of Chemistry and the Materials Science and Engineering Program, Washington State University, Pullman, Washington 99164, United StatesAlex Samuels - †Department of Chemistry and the Materials Science and Engineering Program, Washington State University, Pullman, Washington 99164, United StatesKaty Wisuri - †Department of Chemistry and the Materials Science and Engineering Program, Washington State University, Pullman, Washington 99164, United StatesSarah Landstrom - ‡Department of Physics, Kutztown University, Kutztown, Pennsylvania 19530, United StatesTessa Saul - §Moscow High School, Moscow, Idaho 83843, United States
- Publication Details
- Inorganic chemistry, Vol.54(13), pp.6216-6225
- Academic Unit
- Chemistry, Department of
- Publisher
- United States
- Identifiers
- 99900547692801842
- Language
- English
- Resource Type
- Journal article