The development of ligands that selectively bind to lanthanide (Ln) and/or actinide ions found in nuclear waste is an important area of research. When isolated, lanthanides have various applications such as contrast agents in medical imaging and as advanced luminescent materials. This research focuses on the structural, energetic, and thermodynamic properties of solvated lanthanides in the aqueous and gas phase using computational methods. In the first part of the study, a combined approach using molecular dynamics (MD) and ab initio simulations were used to investigate the behaviors of trivalent lanthanide ions in water. For the MD simulations, a single lanthanide solvated in water was modeled with the12-6-4 LJ-type nonbonded function. Ab initio geometry optimizations were performed using the PBE0 density functional, combined with effective core potentials and the 3-21G* and def2-SVP basis sets. The COSMO solvation model was applied to approximate complexes in the solution phase. Bond distances between the Lns and water oxygens, coordination numbers, and binding energies were reported for Ce3+, Eu3+, Gd3+, and Tb3+ ions. Both computational methods show a decrease in Ln-O distance with decreasing atomic radii. Secondly, we report the selective binding affinities of a tripodal ligand containing three carbamoylmethylphosphine oxide (CMPO) groups attached to a tris(2-aminoethyl)amine (TREN) or a tris(2-aminopropyl)amine (TRPN) cap with lanthanide ions (Ce3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, and Yb3+) in both the aqueous and gas phase. Using the same ab initio methods, the binding energy and free energy were determined. Solvating NO3- ions were also included, and their effects on the binding energy were reported. Our results show that it is energetically favorable for the TREN-CMPO-OEt ligand to bind to, in decreasing order, Dy3+, Tb3+, Yb3+, Ho3+, Eu3+, Gd3+, Ce3+ in the gas phase.

Computational investigation of binding energetics for selective lanthanide extraction

2019 Spring National Meeting

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