On the hardness evaluation in solvent for neutral and charged systems

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Molecular hardness is a key chemical concept, influencing reactivity and stability.
• Understanding solvent effects on molecular properties is crucial for accurate chemical predictions.
• Density functional theory (DFT) provides a robust framework for studying electronic structure and properties.

Purpose of the Study:

• To investigate the influence of water as a solvent on the hardness values of neutral and charged molecules.
• To compare the performance of three different computational methods in predicting solvent effects on molecular hardness.
• To assess the reliability of observed hardness changes using the hard-soft/acid-base (HSAB) principle and reaction free energy calculations.

Main Methods:

• Employed density functional theory (DFT) calculations.
• Utilized the polarizable continuum model (PCM) to simulate solvent effects of water.
• Applied three established working formulas for hardness calculation, comparing gas-phase and solvent-phase results.

Main Results:

• Two of the employed computational methods yielded hardness values that remained unchanged when transitioning from gas phase to solvent phase.
• A third computational method exhibited significant and remarkable changes in molecular hardness upon solvation.
• Reliability checks using the hard-soft/acid-base principle and free energy of reaction calculations supported the observed hardness behaviors.

Conclusions:

• The choice of computational method significantly impacts the prediction of solvent effects on molecular hardness.
• Certain theoretical approaches are more sensitive to environmental changes, highlighting the importance of method selection.
• The study provides insights into the behavior of molecular hardness in aqueous solutions, relevant for chemical reactivity predictions.