Synthesis and study of bistriazolyl-pyrazines as new ligands for An/Ln separations

Herein, we present new hydrophilic tridentate ligands, bistriazolyl pyrazines. Their design was inspired by structurally similar and promising bis-triazolyl-pyridines (PyTri) ligands as well as theoretically derived criteria for the design of tridentate ligands for An/Ln separations suggested by theoretical studies. These ligands have been synthesised, characterised and tested as possible extractants for An/Ln nuclear separations. In addition, UV and fluorescence studies, pKa determination, and crystallographic and theoretical studies have been performed to explain their observed behaviour. Although the results of the solvent extraction studies have shown that these ligands do not possess sufficient selectivity for the extraction of Am vs Eu in i-SANEX conditions, this study presents a valuable test of the criteria for the design of tridentate heterocyclic N-donor ligands for advanced nuclear separation as postulated by theoretical studies a decade ago. Our experimental observations and theoretical studies have found that these criteria might not be the best guidance for designing novel hydrophilic ligands for An/Ln separations in i-SANEX conditions.