Redox chemistry of actinide ions in Wells-Dawson heteropolyoxoanion complexes.
The redox behavior has been characterized for several actinide (An) complexes with the monovacant Wells-Dawson anion, of the form [An{sup n+}({alpha}-2-P{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup n-20} (An = Th{sup 4+}, U{sup 4+}, Np{sup 4+}, Pu{sup 4+}, and Am{sup 3+}). Two complexes, with An = U{sup 4+} and Am{sup 3+}, show redox activity under oxidizing conditions, which is attributed to the actinide oxidation. Am{sup 3+} is oxidized to Am{sup 4+} with an E{sub 1/2} = +1.21{+-}0.01 V, and U{sup 4+} oxidizes to U{sup 5+} with a measured E{sub 1/2} = +0.55{+-}0.01 V vs. Ag/AgCl. Although the cyclic voltammetry (CV) data are consistent with a reversible redox couple, bulk oxidative electrolysis of [U{sup 4+}({alpha}-2-P{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 16-} results in the decomposition of this complex to produce uranyl acetate and the free monovacant Wells-Dawson anion. In contrast, all of the CV data from the actinide coordination complexes differ from equivalent data obtained from the [{alpha}-2-P{sub 2}W{sub 17}O{sub 61}]{sup 10-} ligand itself. There are two complexed An{sup 4+} ions, Np and Pu, that undergo reduction over the same potential range as the ligands themselves. In situ X-ray spectroelectrochemistry is used to quantify the actinide response. The Np{sup 4+}/Np{sup 3+} redox behavior is a classically single ion process, with a formal potential of -0.84{+-}0.01 V that was determined from a Nernst plot of X-ray absorption near-edge structure (XANES) data. The Pu{sup 4+}/Pu{sup 3+} formal reduction potential in the complex [Pu({alpha}-2-P{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup n-} was determined to be -0.17{+-}0.01 V using the same methodology. However, in this latter case, the slope of the Nernst plot indicates that 0.72{+-}0.03 electrons are involved in the reduction. This is a significant deviation from the 1 electron expected for the Pu couple, and is discussed in terms of the concomitant reduction of the P-W-O framework of the Wells-Dawson anion.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); EM
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 961308
- Report Number(s):
- ANL/CHM/JA-46451; EJICFO; TRN: US201011%%581
- Journal Information:
- Eur. J. Inorg. Chem., Vol. 16, Issue Aug. 18, 2003; ISSN 1434-1948
- Country of Publication:
- United States
- Language:
- ENGLISH
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