Rare earth element, or lanthanide, separation techniques such as solvent extraction, froth flotation, or ion exchange, involve lanthanide ions in solution. To predict coordination structures in solution, and thermodynamic properties such as binding energies or acidity constants, of lanthanide-solvent and lanthanide-ligand complexes, it is necessary to consider the electronic structure due to reactions and dynamics to sample molecular conformations. Using a combination of electronic structure calculations, ab initio molecular dynamics simulations, extended X-ray absorption fine structure measurements, and emission spectroscopy, we will describe: i) the solution structures of lanthanide aqua ions; ii) the effect of temperature on the stability of the lanthanide aqua ions in solution; iii) the acidity constants of lanthanide aqua ions; iv) the solution structures of lanthanide-ligand complexes; and v) predicted lanthanide-ligand complex binding energies. Results show that : i) predicted lanthanide aqua ion structures from simulation are within ~0.05 Å of experimental measurements;1ii) the thermal stability of lanthanide aqua ions increases along the lanthanide series; iii) predicted values of the first, second, and third acidity constants are within ~1, ~3, and ~5 pKa units from experiment, respectively;2iv) predicted lanthanide-ligand complex structures from simulation are within ~0.05 Å of experimental measurements;3and v) the relative binding energies of lanthanide-ligand complexes across the lanthanide series can be quantified to replicate experimental trends.

Predicting the coordination structures and thermodynamic properties of lanthanide ions in solution

ACS Spring 2022

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