Spectroscopic study of americium(III) complexes with nitrogen containing organic model ligands

• For the first time, the complex formation of Am(III) with various nitrogen containing humic acid model ligands (anthranilic acid, picolinic acid) was studied.
• With all ligands Am(III) complexes could be identified.
• Spectroscopic characteristics, stability constants as well as stoichiometries of the formed complexes were determined.

For the first time, the complexation of Am(III) with low molecular weight nitrogen containing aromatic model ligands, representing structural building blocks of humic acid, has been investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complex formation with anthranilic acid and picolinic acid was studied at pH 3.8 and 6.0 at an ionic strength of 0.1 M (NaClO4) and room temperature. At pH 3.8, where both investigated ligands occur as zwitterionic species, a 1:1 Am(III) picolinate complex is formed with a stability constant of log β11 = 3.81 ± 0.44. The Am(III) complexation with anthranilic acid in its zwitterionic form seems to be hindered, due to electrostatic repulsion between the protonated amino group and the metal ion. With both ligands, Am(III) complexes could be identified at pH 6.0, where the fully deprotonated species of anthranilic acid and picolinic acid occur. Under the given experimental conditions, a 1:1 Am(III) anthranilate complex with log β11 = 3.70 ± 0.11 is formed. For the Am(III) picolinate system 1:1 and 1:2 complexes with log β11 = 3.83 ± 0.22 and log β12 = 7.34 ± 0.04, respectively, were identified. For comparison, the complex formation of Am(III) was also studied with phthalic acid as an example for the interaction of Am(III) with carboxylic groups.

For the first time, the complex formation of Am(III) with various nitrogen containing humic acid model ligands (anthranilic acid, picolinic acid) was studied. With all ligands Am(III) complexes could be identified. Spectroscopic characteristics, stability constants as well as stoichiometries of the formed complexes were determined.Figure optionsDownload as PowerPoint slide