Fully Chelating N 3 O 2 -Pentadentate Planar Ligands Designed for the Strongest and Selective Capture of Uranium from Seawater.

Based on the unique fivefold equatorial coordination of UO 2 2+ , water-compatible pentadentate planar ligands, H 2 saldian and its derivatives, were designed for the strong and selective capture of UO 2 2+ in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO 3 - /CO 3 2- , pH 8), saldian 2- shows the strongest complexation with UO 2 2+ to form UO 2 (saldian) (log β 11 = 28.05 ± 0.07), which is more than 10 order of magnitude greater than amidoxime-based or -inspired ligand systems most commonly employed for U capture from seawater. Good selectivity for UO 2 2+ from other metal ions coexisting in seawater was also demonstrated.