Time-Resolved Laser Fluorescence Spectroscopy Study of the Coordination Chemistry of a Hydrophilic CHON [1,2,3-Triazol-4-yl]pyridine Ligand with Cm(III) and Eu(III)

The complexation of Cm­(III) and Eu­(III) with the novel i-SANEX complexing agent 2,6-bis­[1-(propan-1-ol)-1,2,3-triazol-4-yl]­pyridine (PTD) was studied by time-resolved laser fluorescence spectroscopy (TRLFS). The formation of 1:3, 1:2, and 1:1 metal/ligand complexes was identified upon increasing PTD concentration in 10^–3 mol/L HClO₄ and in 0.44 mol/L HNO₃ solutions. For all these complexes, stability constants were determined at different acid concentrations. Though under the extraction conditions proposed for an An/Ln separation process, that is, for 0.08 mol/L PTD in 0.44 mol/L HNO₃, 1:3 complexes represent the major species, a significant fraction of 1:2 complexes was found. This is caused by ligand protonation, and results in lower Eu­(III)/Am­(III) separation factors compared to SO₃–Ph–BTP, until now considered the i-SANEX reference ligand. Focused extraction studies performed at lower proton concentration, where the 1:3 complex is formed exclusively, confirm this assumption.