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Journal Articles

Neptunium carbonato complexes in aqueous solution; An Electrochemical, spectroscopic, and quantum chemical study

Ikeda, Atsushi; Tsushima, Satoru*; Takao, Koichiro*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi; Hennig, C.*

Inorganic Chemistry, 48(24), p.11779 - 11787, 2009/12

https://doi.org/10.1021/ic901838r

Times Cited Count：34 Percentile：79.66(Chemistry, Inorganic & Nuclear)

The electrochemical behavior and complex structure of Np carbonato complexes have been investigated in aqueous Na $_{2}$ CO $_{3}$ and Na $_{2}$ CO $_{3}$ /NaOH solutions at different oxidation states by using cyclic voltammetry, X-ray absorption spectroscopy, and density functional theory calculations. The end-member complexes of penta- and hexavalent Np in 1.5 M Na $_{2}$ CO $_{3}$ with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex, [NpO $_{2}$ (CO $_{3}$ ) $_{3}$ ] $^{n-}$ ( = 5 for Np $^{rm V}$ , and 4 for Np $^{rm VI}$ ). In contrast, the electrochemical oxidation of Np $^{rm V}$ in a highly basic carbonate solution of 2.0M Na $_{2}$ CO $_{3}$ /1.0M NaOH (pH 13) yielded a stable heptavalent Np complex of [Np $^{rm VII}$ O $_{4}$ (OH) $_{2}$ ] $^{3-}$ , indicating that the oxidation reaction from Np $^{rm V}$ to Np $^{rm VII}$ in the carbonate solution involves a drastic structural rearrangement from the transdioxo configuration to a square-planar-tetraoxo configuration, as well as exchanging the coordinating anions from carbonate ions (CO $_{3}$ $^{2-}$ ) to hydroxide ions (OH $^{-}$ ).

Journal Articles

Structural determination of neptunium redox species in aqueous solutions

Ikeda, Atsushi; Hennig, C.*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi

ESRF Highlights 2008, p.99 - 100, 2009/02

Structural arrangement of Np species has been investigated in various aqueous solutions by synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy. The obtained results revealed that Np(IV) dominantly forms a spherically coordinated decahydrate complex, [Np(H $_{2}$ O) $_{20}$ ] $^{4+}$ , while Np(V) and -(VI) form a pentahydrate neptunyl complex, [NpO $_{2}$ (H $_{2}$ O) $_{5}$ ] $^{n+}$ .

Journal Articles

Electrochemical and complexation behavior of neptunium in aqueous perchlorate and nitrate solutions

Ikeda, Atsushi; Hennig, C.*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi

Inorganic Chemistry, 47(18), p.8294 - 8305, 2008/09

https://doi.org/10.1021/ic8009095

Times Cited Count：82 Percentile：68.72(Chemistry, Inorganic & Nuclear)

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption and Np L $_{rm III}$ -edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo the structural rearrangement from spherical coordinating ions (Np $^{3+}$ and Np $^{4+}$ ) to transdioxo neptunyl ions (NpO $_{2}$ $^{n+}$ , n = 1 for Np(V) and 2 for Np(VI)). A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H $_{2}$ O) $_{10}$ ] $^{4+}$ in 1.0 M HClO $_{4}$ , while Np(V) and -(VI) exist dominantly as pentaaquo neptunyl complexes, [NpO $_{2}$ (H $_{2}$ O) $_{5}$ ] $^{n+}$ (n = 1 for Np(V) and 2 for Np(VI)).