The structural and kinetic studies of U(VI) complex with benzamidoxime (Hba) as ligand in CD3COCD3 have been studied by means of 1H and13 C NMR. The Hba molecule was found to coordinate to UO2+2 in the form of anionic benzamidoximate (ba), and the number of ba coordinated to UO2+2 was determined to be 3 by analyzing the chemical shift of 13C NMR signal for Hba in the presence of UO2+2. The exchangerate constants (kex) of ba in [UO2(ba)3]− were determinedby the NMR line-broadening method. The kinetic parameterswere obtained as follows: kex(25°C)=1.3×103 s-1, ΔH≠ =35.8±3.5kJ·mol-1, and ΔS≠=-65±13.7 J·K-1·mol-1. The UV-visible absorption spectra of solutionscontaining UO2+2 and Hba were also measured. The molar extinction coefficient of the complex wasfound to be extremely large compared with those of UO2(L)2+5 (L=unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of UO2+2 from Hba and suggests that an interaction between UO2+2 and Hba is very strong. Such a high affinity of monomericamidoxime to UO2+2 reasonably explains the high adsorptivity of amidoxime resin to U(VI) species, and is considered to result in the high recovery of U(VI) species from sea water using amidoxime resin.
ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Nuclear Energy and Engineering