Koichiro Takao, Masaru Kato, Shinobu Takao, Akira Nagasawa, Andreas C. Scheinost, Gert Bernhard, Christoph Hennig, Yasuhisa Ikeda
ACTINIDES 2009 9 (1) 1757-8981 2010
[Refereed][Not invited] A U(VI) complex with N,N'-disalicylidenediethylenetriaminate (saldien(2-)) was characterized by single crystal X-ray analysis and X-ray absorption fine structure (XAFS) spectroscopy, and its electrochemical behavior in a DMSO solution was studied. The obtained U(VI)-saldien(2-) complex recrystallized from DMSO was identified as orthorhombic (UO2)-O-VI(saldien)center dot DMSO. All coordination sites in the equatorial plane of UO22+ are occupied by coordinating O and N atoms of saldien(2-). Comparing a k(3)-weighted U L-III-edge EXAFS spectra of (UO2)-O-VI(saldien) in DMSO and DMF solutions with that in solid state, the molecular structure of (UO2)-O-VI(saldien) remains even in the solutions. Quasi-reversible redox waves of (UO2)-O-VI(saldien) were observed at E degrees = -1.582 +/- 0.005 V vs. Fc/Fc(+) (Delta E-p = 0.080-0.170 V at v = 0.010-0.500 V.s(-1)) in DMSO. UV-Vis-NIR absorption spectral change with the electrochemical reduction of (UO2)-O-VI(saldien) using the spectroelectrochemical technique shows isosbestic points clearly, indicating that the electrochemical reaction of (UO2)-O-VI(saldien) is only present. Using the absorbance change and the Nernstian equation, the electron stoichiometry in the reduction of (UO2)-O-VI(saldien) in DMSO was determined as 0.929. This quantity close to unity reveals a redox reaction, (UO2)-O-VI(saldien) + e(-) = [(UO2)-O-V(saldien)](-), i. e., (UO2)-O-VI(saldien) without unidentate ligands results in the stable U(V) complex, [(UO2)-O-V(saldien)](-), in DMSO. This U(V) species also shows the characteristic absorption bands of U(V) at 630, 700, 830, 1390, and 1890 nm as well as other U(V) complexes.