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

Based on unique 5-fold equatorial coordination of UO22+, water-compatible pentadentate planar ligands, H2saldian and its derivatives, were designed as 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 = 27.5), 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.