The Sulfate coordination of Np(IV), Np(V), and Np(VI) in aqueous solution

Hennig, C.*; Ikeda, Atsushi ; Tsushima, Satoru*; Scheinost, A. C.*

Coordination and redox behavior of Np(IV), Np(V) and Np(VI) sulfate in aqueous solution has been investigated by Np L3-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, cyclic voltammetry and density functional theory (DFT) calculations. TNp(VI) is coordinated by sulfate in bidentate (RNp-S = 3.12 A) and monodentate (RNp-S = 3.61 A) modes at a low sulfate concentration of [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] = 1. At higher [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] ratios bidentate coordination prevails. Approximately two bidentate sulfate groups are coordinated to Np(VI) at 2.0 M SO $_{4}$ $^{2-}$ and pH 1.1. Np(V) is coordinated by sulfate in bidentate (RNp-S = 3.16 A) and monodentate (RNp-S = 3.67 A) modes. However, sulfate coordination is less pronounced here and does not exceed in total one SO $_{4}$ $^{2-}$ ligand in a solution of 2.0 M SO $_{4}$ $^{2-}$ . The redox couple Np(VI)/Np(V) is reversible at low [SO $_{4}$ $^{2-}$ ]/[NpO $_{2}$ $^{2+}$ ] ratio and becomes irreversible at high sulfate concentration due to structural rearrangement of the sulfate ligands.

Language	:	English
Journal	:	Inorganic Chemistry
Volume	:	48
Number	:	12
Pages	:	p.5350 - 5360
Publication Year/Month	:	2009/06
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Paper URL	:	https://doi.org/10.1021/ic9003005
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Keywords	:	no keyword
Research Facility	:	SPring-8(大型放射光施設)
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Article of JAEA R&D Review	:
Cooperating Institute	:	Forschungszentrum Dresden-Rossendorf

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Registration No. : AA20090109
JAEA Abstracts No. : 37000834
Paper Submission No. : 5858

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