Unexpected Solute Occupancy and Anisotropic Polarizability in Lewis Basic Solutions

Area of Science:

• Computational chemistry
• Physical chemistry
• Solution chemistry

Background:

• Understanding solvation structures of alkali metal hydroxides is crucial for chemical processes.
• Previous studies have focused on bulk properties, with limited insight into specific cation-water interactions.

Purpose of the Study:

• To elucidate the solvation structure of YOH (Y = Li, Na, K) using density functional computation.
• To investigate the influence of alkali metal cations on water molecule orientation and hydrogen bonding.

Main Methods:

• Density functional theory (DFT) computations were employed to model YOH solvation.
• Analysis of cation-water interactions, including repulsion and attraction, was performed.
• Spectroscopic confirmation of predicted structural and bonding changes.

Main Results:

• Alkali metal cations (Y+) were found to reside eccentrically in interstitial hollow sites, forming Y+·4H2O units.
• Hydroxide ions (OH-) formed OH-·H2O units, with the hydroxide ion at the center.
• Repulsive Y+↔H+ and attractive Y+:O2- interactions caused anisotropic polarization of the Y+ cation and structural distortions.

Conclusions:

• The solvation structure of YOH is characterized by eccentric cation dislocation and altered hydrogen bonding networks.
• Anisotropic cation polarizability and solute bonding network distortions impact phonon frequencies.
• Computational findings were spectroscopically validated, confirming the proposed solvation models.