Sequestering uranium from seawater: binding strength and modes of uranyl complexes with glutarimidedioxime

Abstract

Glutarimidedioxime (H₂A), a cyclic imide dioxime ligand that has implications in sequestering uranium from seawater, forms strong tridentate complexes with UO₂²⁺. The stability constants and the enthalpies of complexation for five U(VI) complexes were measured by potentiometry and microcalorimetry. The crystal structure of the 1 : 2 metal–ligand complex, UO₂(HA)₂·H₂O, was determined. The re-arrangement of the protons of the oxime groups (–CHN–OH) and the deprotonation of the imide group (–CH–NH–CH–) results in a conjugated system with delocalized electron density on the ligand (–O–N–C–N–C–N–O–) that coordinates to UO₂²⁺via its equatorial plane.