Complexation of uranyl with chelidamic acid: Crystal structures, binding strength, and electrochemical redoxes

Chelidamic acid (denoted as H3L in this paper) is a naturally occurring derivative of dipicolinic acid that functions as a versatile ligand. The complex formation of chelidamic acid with UO22+ has been investigated by potentiometry in a 0.1 M NaClO4 solution. The potentiometry identified 1:1 uranyl–chelidamate complexes (UO2HL, UO2L2−), 1:2 uranyl–chelidamate complex (UO2L24−), and a hydrolytic complex UO2(OH)2L2−. The possible UO2H2L22− structure was determine by crystal analysis. Chelidamate molecules coordinate to uranyl mainly through the pyridine–carboxylate chelation pocket (O, N, O), and 4-pyridinol–OH group is protonated. The presence of hydrolysate UO2(OH)2L2– was further confirmed by nuclear magnetic resonance spectroscopy (NMR). In an alkaline aqueous medium under anaerobic conditions, the complex UVIO2(OH)2L2−can be electrochemically reduced to pentavalent uranyl.