Piperazinyl-Based Diamide Ligand for Selective Precipitation of Actinyl (UO₂²⁺/PuO₂²⁺) Ions with Fast Kinetics

Abstract

A novel ligand N,N′-bis(N″,N″-diethyl carbamoyl) piperazine (BDECP), L1, is synthesized as a selective precipitant for hexavalent actinyl (UO 2 2+ and PuO 2 2+) ions from an aqueous nitric acid medium. The ligand BDECP forms an infinite one-dimensional coordination polymer with uranyl nitrate and behaves as a bridging bidentate neutral donor. There is an alternate repetition of [UO 2 (NO 3 ) 2 ] and BDECP units as evidenced by single-crystal Xray diffraction. Uranyl ion (UO 2 2+ ) can be precipitated in >99% yield from an aqueous nitric acid medium. L1 shows fast kinetics of precipitation of uranyl ion as compared to those of other reported ligands like N-alkyl pyrolidone and N-(1-adamantyl) acetamide. Avrami's coefficient, obtained from the Avrami− Erofe'ev equation, shows that the precipitation mechanism is controlled by the phase boundary and not governed by diffusion. Theoretical studies of the uranyl complex of L1 show that there is no thermodynamic preference for L1 as compared to other potential amide-based precipitants. The principal factors that govern the fast kinetics of precipitation are the aqueous solubility and higher charge density on the amide oxygen of L1.

Effects of coordinating heteroatoms on molecular structure, thermodynamic stability and redox behavior of uranyl(vi) complexes with pentadentate Schiff-base ligands

“…Hence, the complexation between UO 2 2+ and organic ligands has been widely studied. [1][2][3][4][5][6][7][8][9][10][11][12][13] Pearson's Hard and So Acids and Bases (HSAB) principle is quite useful to describe preferential interactions between specic metal ions and coordinating atoms of ligands and to design organic molecules selectively coordinating with a target metal ion, 14,15 although this principle is rather empirical. In the HSAB principle, UO 2 2+ is classied as a hard acid, 14,15 and therefore, generally tends to more strongly interact with hard bases like N, O and F, compared with soer ones such as heavier congeners like P, S, and Cl.…”