Theoretical prediction of electronically modulated pentadentate ligands for extraction uranium from seawater

At present, the development of efficient adsorption functional groups is essential for uranium extraction from seawater. In this work, the complexation of uranyl ions with a series of electronically modulated N3O2-pentadentate planar ligands (H2L) has been explored by quantum chemical calculations. All the modified ligands are found to be fully chelated with the uranyl ions, forming the fivefold equatorial coordinated extraction complexes, which indicates that the introduction of substituents has little effect on the coordination of the ligands. The H2L3 ligand with the strong electron-donating methoxy group substituted to ortho-phenol demonstrates stronger covalent bonding toward uranyl ions. Consequently, H2L3 possesses higher complexation capacity than other ligands, which may have potential application in uranium extraction from seawater. Conversely, the substitution on the amino groups seems to be not conducive to increasing the affinity of ligands for uranyl ions, and the complexing capacity of the ligands is reduced for substituents with weaker electron-donating ability. This work gives an insight into the extraction behaviors of different N3O2-pentadentate derivatives with uranyl ions, and provides a theoretical basis for the design and development of multidentate ligands for seawater uranium recovery.