Investigation of f-Element Interactions with Functionalized Diamides of Phenanthroline-Based Ligands

Separations relevant to trivalent actinides and lanthanides have been a focus of the f-element community in the past few decades. A central focus of this effort has been optimizing ligands for separations. From a fundamental perspective, one must investigate the metal-ligand interactions for optimal ligand design. A well-explored class of ligands, phenanthroline diamides, is reviewed to further elucidate the actinide or lanthanide-ligand interactions of primarily Am3+, Cm3+, and Eu3+. Mixed nitrogen and oxygen donors of this nature are of interest to explore due to their increased selectivity for the trivalent actinides over the trivalent lanthanides. Phenanthroline diamide ligands have shown to have promise in industrial-scale separations compared to bipyridine and pyridine diamide ligands with larger selectivity for the trivalent actinides. These interactions are studied through solvent extraction, spectroscopic, and thermodynamic techniques. Further analysis provided in this review includes an overview of the computational results provided and relevant comparisons to experimental data. The computational parameters considered are the calculated bond lengths, thermodynamic parameters, and values that provide insight to a discussion of covalent interactions between metal and ligand. The information provided is important to benchmark the state-of-the-art basic, applied, and computational chemistry of the phenanthroline diamide class of ligands.