Neptunium carbonato complexes in aqueous solution; An Electrochemical, spectroscopic, and quantum chemical study
水溶液中のネプツニウム炭酸錯体に関する電気化学,分光学、及び量子化学的研究
池田 篤史
; 津島 悟*; 鷹尾 康一朗*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; 矢板 毅; Hennig, C.*
Ikeda, Atsushi; Tsushima, Satoru*; Takao, Koichiro*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi; Hennig, C.*
水溶液中で形成されるネプツニウム(Np)の炭酸錯体について、電気化学的手法,紫外可視・赤外分光法,X線吸収分光法、及び量子化学計算を用いて、その電気化学的及び錯体化学的特性を検討した。その結果、V価及びVI価のNpは1.5M Na
CO
溶液中においてネプツニル三炭酸錯体である[NpO
(CO
)
]
を形成していること、さらにpH=13以上の2.0M Na
CO
/1.0M NaOH溶液中ではNp(V)は電気的にNp(VII)まで酸化され、劇的な錯体構造の変化を伴い[NpO
(OH)
]
を形成していること等が明らかとなった。
The electrochemical behavior and complex structure of Np carbonato complexes have been investigated in aqueous Na
CO
and Na
CO
/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
CO
with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex, [NpO
(CO
)
]
(
= 5 for Np
, and 4 for Np
). In contrast, the electrochemical oxidation of Np
in a highly basic carbonate solution of 2.0M Na
CO
/1.0M NaOH (pH
13) yielded a stable heptavalent Np complex of [Np
O
(OH)
]
, indicating that the oxidation reaction from Np
to Np
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
) to hydroxide ions (OH
).