Fully Chelating N3O2-Pentadentate Planar Ligands Designed for the Strongest and Selective Capture of Uranium from Seawater.

Based on the unique fivefold equatorial coordination of UO22+, water-compatible pentadentate planar ligands, H2saldian and its derivatives, were designed for the strong and selective capture of UO22+ in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO3-/CO32-, pH 8), saldian2- shows the strongest complexation with UO22+ to form UO2(saldian) (log β11 = 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 UO22+ from other metal ions coexisting in seawater was also demonstrated.