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Raman Spectral Titration Method:Informative Technique for Studying Complexation of Uranyl with Uranyl(VI)-DPA/Oxalate Systems as Examples

Abstract

The Raman band at about 870 cm-1 originated from the symmetric stretch vibration (ν1) of uranyl, UO22+, is proven to be very informative for investigating the complexation of uranyl using perchlorate or nitrate of known concentration as internal standards. The concentration of uranyl can be conveniently calculated by the ratio of the directly read band intensities of uranyl and the added reference, ClO4-, with a factor of 1.72. While with nitrate NO3- of lower than 1.8 M as reference, a factor of 0.85 should be used. Further, with added internal standards, the linear relationship between the Raman intensity and the concentration of the corresponding species is illustrated by spectral titration of U(VI) with a very strong ligand, dipicolinic acid (DPA); and the application of spectral titration method with Raman spectroscopy in studying the complexation of uranyl is demonstrated by the titration of U(VI) with oxalate. The stepwise changes in Raman shift of 18, 17, and 6 cm-1, coorsponding to the three oxalate anions successively bonding to UO22+, imply that the coordination modes are different. In the 1:1 and 1:2 of metal to ligand complexes, the oxalate anions bond to the uranyl ion in side-on bidentate mode, but in the 1:3 complex the third oxalate bonds in head-to mode, which is much weaker than the first two.

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Publication details

The article was received on 04 May 2017, accepted on 13 Jun 2017 and first published on 13 Jun 2017


Article type: Paper
DOI: 10.1039/C7DT01631J
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Raman Spectral Titration Method:Informative Technique for Studying Complexation of Uranyl with Uranyl(VI)-DPA/Oxalate Systems as Examples

    Q. Liu, Q. Zhang, S. Yang, H. Zhu, Q. Liu and G. Tian, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT01631J

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