Uranyl Affinity between Uranyl Cation and Different Kinds of Monovalent Anions: Density Functional Theory and Quantitative Structure-Property Relationship Model.

ABSTRACT

In order to design effective extractants for uranium extraction from seawater, it is imperative to acquire a more comprehensive understanding of the bonding properties between the uranyl cation (UO22+) and various ligands. Therefore, we employed density functional theory to investigate the complexation reactions of UO22+ with 29 different monovalent anions (L-1), exploring both mono- and bidentate coordination. We proposed a novel concept called "uranyl affinity" (Eua) to facilitate the establishment of a standardized scale for assessing the ease or difficulty of coordination bond formation between UO22+ and diverse ligands. Furthermore, we conducted an in-depth investigation into the underlying mechanisms involved. During the process of uranyl complex [(UO2L)+] formation, lone pair electrons from the coordinating atom in L- are transferred to either the lowest unoccupied molecular degenerate orbitals 1ϕu or 1δu of the uranyl ion, which originate from the uranium atom's 5f unoccupied orbitals. In light of discussion concerning the mechanisms of coordination bond formation, quantitative structure-property relationship analyses were conducted to investigate the correlation between Eua and various structural descriptors associated with the 29 ligands under investigation. This analysis revealed distinct patterns in Eua values while identifying key influencing factors among the different ligands.