Predicting hydration energies for multivalent ions.

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Solution Chemistry

Background:

• Accurate prediction of ion hydration free energies is crucial for understanding chemical processes.
• Existing computational methods have limitations in predicting these energies, particularly for multivalent ions.

Purpose of the Study:

• To predict the free energy of hydration for 40 monovalent and multivalent cations and anions.
• To evaluate the performance of density functional theory combined with COSMO-RS against experimental data.

Main Methods:

• Utilized density functional theory (DFT) with Becke-Perdew (BP)/Triple zeta valence with polarization functions (TZVP) level.
• Employed the implicit solvent model COnductor like Screening MOdel for Real Solvents (COSMO-RS).
• Included one hydration shell of explicit water molecules for metal cations.

Main Results:

• Good agreement with experimental data for monovalent and divalent ions, outperforming standard COSMO.
• Slightly worse agreement and systematic errors observed for trivalent and tetravalent ions.
• The method demonstrates reliability for multivalent ions when explicit water molecules are included.

Conclusions:

• Quantum chemical calculations with COSMO-RS offer a reliable approach for studying multivalent ions in solution.
• The low computational cost enables investigation of trends, particularly in ligand exchange reactions.
• While not precise enough for absolute predictions, the method is valuable for relative energy studies.