Trivalent Actinide and Lanthanide Separation by Derivatives of INVEST Species

Abstract

We employed scalar-relativistic density functional theory (DFT) to compute the binding free energies (ΔG) for the coordination of Am³⁺ and Eu³⁺ with four previously reported 1,10-phenanthroline ligands (L1-L4). Among these, L1 and L4, which have been previously characterized experimentally, exhibited the highest ΔΔG values, representing the differential binding between Am³⁺ and Eu³⁺. These values were then used as a baseline to assess the Am³⁺/Eu³⁺ separation capabilities of newly investigated derivatives of triangulenes, molecules of interest due to their inverted singlet–triplet (INVEST) gaps. Notably, two of these ligands exhibited ΔΔGs exceeding those of L1/L4 by up to 1.4 kcal/mol, suggesting an order-of-magnitude improvement in separation factors while maintaining similar binding affinities for Am³⁺. These findings indicate that INVEST-based ligands hold significant promise for the next generation of Am³⁺/Eu³⁺ extractants.