Complex Formation of U(VI) with Benzamidoxime in Non-aqueous Solvents

Abstract

Abstract The structural and kinetic studies of U(VI) complex with benzamidoxime (Hba) as ligand in CD3COCD3 have been studied by means of 1H and 13 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 exchange rate constants (kex) of ba in [UO2(ba)3]- were determined by the NMR line-broadening method. The kinetic parameters were 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 solutions containing UO2+ 2 and Hba were also measured. The molar extinction coefficient of the complex was found 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 monomeric amidoxime 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. KEYWORDS: uranium(VI) ionuranyl-benzamidoxime complexligandsexchange interactionsnuclear magnetic resonancechelating resinamidoxime resinresins