Liu Qian, Zhang Qianci, Yang Suliang, Zhu Haiqiao, Liu Quanwei, Tian Guoxin
Department of Radiochemistry, China Institute of Atomic Energy, Beijing, 102413, China.
Dalton Trans. 2017 Oct 10;46(39):13180-13187. doi: 10.1039/c7dt01631j.
The Raman band at about 870 cm originating from the symmetric stretch vibration (ν) of uranyl, UO, has 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 using the ratio of the directly read band intensities of uranyl and the added reference, ClO, with a factor of 1.72. While with NO of concentration lower than 1.8 M as the reference, a factor of 0.85 should be used. Furthermore, with added internal standards, the linear relationship between the Raman intensity and the concentration of the corresponding species is illustrated by the spectral titration of U(vi) with a very strong ligand, dipicolinic acid (DPA); and the application of a 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 the Raman shift of 18, 17, and 6 cm, corresponding to the three oxalate anions successively bonding to UO, imply that the coordination modes are different. In the 1 : 1 and 1 : 2 ratios 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-on mode, which is much weaker than the first two.
源于铀酰（UO）对称伸缩振动（ν）的约870 cm处的拉曼带，已被证明对于使用已知浓度的高氯酸盐或硝酸盐作为内标来研究铀酰的络合非常有信息价值。通过使用铀酰与添加的参比物ClO的直接读取的谱带强度之比，并乘以1.72的系数，可以方便地计算出铀酰的浓度。而当使用浓度低于1.8 M的NO作为参比物时，则应使用0.85的系数。此外，添加内标后，通过用非常强的配体二吡啶甲酸（DPA）对U(vi)进行光谱滴定，说明了拉曼强度与相应物种浓度之间的线性关系；并且通过用草酸盐滴定U(vi)，证明了拉曼光谱法在研究铀酰络合中的光谱滴定方法的应用。对应于三个草酸根阴离子相继与UO键合的拉曼位移的18、17和6 cm的逐步变化，意味着配位模式不同。在金属与配体络合物的1∶1和1∶2比例中，草酸根阴离子以侧基双齿模式与铀酰离子键合，但在1∶3络合物中，第三个草酸根以端基模式键合，其强度比前两个弱得多。
