H-bonding competition and clustering in aqueous LiI

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Solution Chemistry

Background:

• Understanding ion-water interactions is crucial for chemical processes.
• The structure and dynamics of hydrogen bond networks in electrolyte solutions are complex.
• Lithium iodide (LiI) is an important electrolyte with unique solvation properties.

Purpose of the Study:

• To characterize the structure and dynamics of the hydrogen bond network in solvated LiI.
• To investigate the effects of salt concentration on LiI solutions.
• To elucidate the interplay between lithium (Li+) and iodide (I-) ions on the water network.

Main Methods:

• First-principles molecular dynamics (MD) simulations at ambient temperature.
• Analysis of structural properties, including solvation shells and ion pairing.
• Calculation and comparison of experimental and simulated Nuclear Magnetic Resonance (NMR) chemical shifts.

Main Results:

• Qualitative differences in hydrogen bond networks at low (1 M) and high (9 M) LiI concentrations.
• Formation of fused Li(+) solvation shells and (Li(+)·H2O)n chains at 9 M.
• Weakening of the hydrogen bond network around I(-) ions, with chaotropic I(-) effects extending further than kosmotropic Li(+) effects.

Conclusions:

• High LiI concentrations promote chain formation over ion pairing.
• I(-) ions act as chaotropes, disrupting the hydrogen bond network, while Li+ ions act as kosmotropes, structuring water locally.
• The study provides insights into the concentration-dependent behavior of LiI in aqueous solutions.