Solvent Phase Optimizations Improve Correlations with Experimental Stability Constants for Aqueous Lanthanide Complexes

ABSTRACT

Stability constants provide insight into ion complexation in water. While computational studies have been shown to model the energy of the complexation successfully using a thermodynamic cycle approach, it does not extend to calculating the stability constants for 1:1 lanthanide to ligand complexes in solution. Using B3LYP and 6-31+G* Pople basis with small core effective core potential (ECP) on the lanthanum ion, and a solvent model based on the full solute electron density (SMD) solvation model we computed and compared with previously published stability constants of the ligands: acetate, acetohydroximate, acetylacetonate, methanoate, tropolonate, hydroxide, catecholate, malonate, oxalate, phthalate, and sulfate. The best R² values for the thermodynamic cycle can only be determined by separating the mono and divalent ions to achieve an R² value of 0.86 and 0.74 for mono and divalent ions, respectively. We show that by optimizing the lanthanide-ligand structures in implicit solvent, we achieve an improved correlation between experimental and computed stability constants of R² value of 0.89 for the combined mono and divalent ions.

KEYWORDS:

• Solvent extraction
• modeling and simulation
• thermodynamics
• extractants
• complexants

Acknowledgments

The authors thank Dr. Benjamin P. Hay for his guidance, Prof. Mark S. Gordon, and Dr. Federico Zahariev for their advice and scientific discourse.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/07366299.2022.2160646

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work is supported by the Critical Materials Institute, an Energy Innovation Hub funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. The research was performed at the Ames Laboratory, which is operated for the US DOE by Iowa State University under [Contract No. DE-AC02-07CH11358]. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a US DOE Office of Science User Facility operated under [Contract No. DE-AC02-05CH11231].