The structural and kinetic studies of U(VI) complex with benzamidoxime (Hba) as ligand in CD3COCD3 have been studied by means of 1 H and 13 C NMR. The Hba molecule was found to coordinate to uo;+ in the form of anionic benzamidoximate (ba), and the number of ba coordinated to uo;+ was determined to be 3 by analyzing the chemical shift of 13 C NMR signal for Hba in the presence of uo;+. The exchange rate constants (kex) of ba in [U02(ba)3J-were determined by the NMR line-broadening method.The kinetic parameters were obtained as follows: kex(25°C)=l.3x10 3 s-1, LlH"=35.8±3.5kJ·mol-1 , and LlS°'=-65±13.7 J-K-1 -mol-1 . The UV-visible absorption spectra of solutions containing uo~+ and Hba were also measured. The molar extinction coefficient of the complex was found to be extremely large compared with those of U02(L);+ (L=unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of uo;+ from Hba and suggests that an interaction between uo;+ and Hba is very strong. Such a high affinity of monomeric amidoxime to uo~+ 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.
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