(86g) Predicting the Structure of Lanthanide-Ligand Complexes in Solution with Ab Initio Molecular Dynamics

Rare earth elements, or lanthanides, are critical in many clean energy and defense technologies. Lanthanide-ligand complex structures are relevant to their separation by solvent extraction. We recently published lanthanide norm-conserving pseudopotentials and basis sets optimized for the generalized gradient approximation and exchange correlation functionals for density functional theory calculations of large systems, which can replicate lanthanide reaction energies and molecular geometries. These allowed us to perform ab initio molecular dynamics simulations of lanthanide aqua ions with explicit solvent molecules. Results agree with experiment showing coordination numbers of nine and eight for the early and late lanthanides respectively, and lanthanide-oxygen radial pair distributions are within 0.05 Å of experimental values. The first coordination shell shows a dynamic equilibrium and not a rigid geometry. Preliminary results also show that we are replicating lanthanide-ligand structures. Our simulations predict the known europium-EDTA coordination structure in basic conditions, with both nitrogen atoms and four EDTA oxygen atoms (one per carboxylate) coordinated to Eu, and an additional three coordinated water molecules. More importantly, the predicted Eu-O and Eu-N distances are within ~0.05 Å of X-ray absorption experiments. Currently, we are exploring the binding behavior of phytosiderophore ligands; preliminary computational and experimental results show lanthanide binding.Our results strongly suggest that we can obtain meaningful structures of lanthanide-ligand complexes in the condensed phase. We report a computational capability that can accurately model lanthanide-ligand complex structures and reactions in the solution phase.