Diglycolamide-functionalized poly(propylene imine) diaminobutane dendrimers for sequestration of trivalent f-elements: synthesis, extraction and complexation

Three diglycolamide-functionalized poly(propylene imine) diaminobutane dendrimers, viz., zero generation (L_I), first generation (L_II), and second generation (L_III), were synthesized and evaluated for their complexation ability towards trivalent actinides and lanthanides. The distribution coefficient (D) of Am³⁺ with 1.0 mmol L⁻¹ ligand in 3 M HNO₃ follows the order: 0.1 (L_I) < 42 (L_II) < 110 (L_III). Slope analysis indicated the stoichiometry of the extracted complexes as: 1 : 2 (M : L) for L_I and 1 : 2 (M : L) for both L_II and L_III. A complexation study of a representative lanthanide (Eu³⁺) with the three ligands by absorption spectroscopy and luminescence spectroscopy confirmed the formation of the above stoichiometry. The stability constants (log β) for the ML complexes of Eu³⁺ with the three ligands were determined to be 5.2 ± 0.03, 5.3 ± 0.01, and 5.4 ± 0.02 for L_I, L_II, and L_III, respectively. The identical log β values (within experimental error) for all the ligands indicate that the complexation is not affected by the branching of the ligands. The metal/ligand complex formation was explained with the help of spectroscopic data.