Solvent extraction and lanthanide complexation studies with new terdentate ligands containing two 1,3,5-triazine...

Area of Science:

• Coordination Chemistry
• Radiochemistry
• Materials Science

Background:

• Separation of trivalent actinides and lanthanides is crucial for nuclear fuel reprocessing and waste management.
• Developing efficient extractants for selective metal ion separation remains a significant challenge in radiochemistry.

Purpose of the Study:

• To evaluate the solvent extraction capabilities of pyridine-triazine ligands, specifically L(5) and L(4), for Am(III) and Eu(III) separation.
• To investigate the structural properties of these ligands and their metal complexes to understand extraction mechanisms.
• To compare the performance of L(5) and L(4) with previously studied ligands like L(1).

Main Methods:

• Solvent extraction experiments using 2,6-bis(4,6-di-pivaloylamino-1,3,5-triazin-2-yl)-pyridine (L(5)) and 2,6-bis(4,6-di-amino-1,3,5-triazin-2-yl)-pyridine (L(4)) with Am(III) and Eu(III) in nitric acid solutions.
• Synergistic extraction studies with 2-bromodecanoic acid.
• Crystallographic analysis of L(5) and the Yb(III)-L(4) complex.
• Theoretical calculations of electronic properties.

Main Results:

• Ligand L(5) demonstrated modest Am/Eu separation factors (SFs) of 2.4-3.7 with a synergist and 4-6 without, from varying nitric acid concentrations.
• L(5) was found to be unstable, degrading to L(4) during complexation.
• The crystal structure of Yb(III)-L(4) revealed a 9-coordinate ytterbium ion.
• L(4) and L(5) exhibited significantly lower SFs compared to L(1) (SF ~140).

Conclusions:

• The pyridine-triazine ligands L(4) and L(5) possess limited efficacy for Am/Eu separation compared to related compounds.
• The poor extraction performance of L(4) and L(5) is attributed to their electronic charge distribution, similar to terpyridine.
• The superior separation properties of L(1) likely stem from the presence of adjacent nitrogen atoms within the triazine rings.