Complexation of Am(III) with Hydrophilic N,N-Dimethyl-Diglycolamic Acid in Aqueous Solution Correlating Extraction...

A comparative study of Am(III) complexation with two structurally similar multidentate acidic ligands─N,N-dimethyl-diglycolamic acid (HDMDGA, HL) and N,N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA, HL')─was conducted from thermodynamic and structural perspectives. Three species (AmL²⁺, AmL₂⁺, and AmL_3(aq.)) were identified in 1.0 mol L^-1 NaClO₄ across the experimental pH range; their stability constants and absorption spectra were also determined. Single crystals of AmL_3(cry.) were prepared by slow evaporation and analyzed by single-crystal X-ray diffraction, revealing a nine-coordinate Am(III) center surrounded by three tridentate L^- ligands. To elucidate the coordination geometry of HL'-extracted complexes, the absorption spectrum of the Am(III)-loaded organic phase was compared with the deconvoluted spectrum of aqueous AmL₃ and the diffuse reflectance spectrum of solid AmL_3(cry.). The spectral similarities indicate that the dominant extracted species, AmL'_3(org.), adopts a nine-coordinate geometry closely resembling that of AmL₃ in both aqueous solution and the solid state.