Structural Determination of Individual Chemical Species in a Mixed System by Iterative Transformation Factor Analysis (ITFA)-based X-ray Absorption Spectroscopy Combined with UV-Visible Absorption and Quantum Chemical Calculation


Structural Determination of Individual Chemical Species in a Mixed System by Iterative Transformation Factor Analysis (ITFA)-based X-ray Absorption Spectroscopy Combined with UV-Visible Absorption and Quantum Chemical Calculation

Ikeda, A.; Hennig, C.; Rossberg, A.; Tsushima, S.; Scheinost, A. C.; Bernhard, G.

A multi-technique approach using UV-visible absorption spectroscopy, EXAFS spectroscopy combined with the factor analysis based on iterative target testing (ITT), and DFT calculations has been performed in order to investigate the speciation of uranium(VI) nitrate species in acetonitrile and to identify the complex structure of each fundamental species in the system. UV-visible spectral titration suggests that there are four different species in the system, that is, pure solvated species, mono-, di-, and trinitrate species. ITT-based factor analysis extracts the pure EXAFS spectra of fundamental species from the measured spectral mixtures on the basis of the speciation diagram calculated from the UV-visible data. Data analysis of the extracted EXAFS spectra and DFT calculations provide the most probable complex structures of fundamental species. That is, the pure solvated species corresponds to a 5-fold uranyl hydrate complex of [UO2(H2O)5]2+. Nitrate ions tend to coordinate to the uranyl(VI) ions with a bidentate fashion rather than a unidentate one in acetonitrile. The mononitrate species forms a 5-fold complex of [UO2(H2O)3NO3]+, while the di- and trinitrate species show a 6-fold complex arrangement, corresponding to [UO2(H2O)2(NO3)2]0 (D2h) and [UO2(NO3)3]- (D3h), respectively. This study demonstrates that the combination of UV-visible absorption and EXAFS spectroscopies with DFT calculations is very powerful for the structural determination of individual species in the mixed system, in which several different species coexist together.

Keywords: Uranium; Nitrate; Acetonitrile; UV-visible; EXAFS; DFT calculations; Factor analysis; Speciation; Complex structure

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Publ.-Id: 10457