Tipping the Balance between S-π and O-π Interactions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Organic Chemistry

Background:

• Non-covalent interactions are crucial in molecular recognition and self-assembly.
• Understanding the subtle differences between sulfur-π (S-π) and oxygen-π (O-π) interactions is key to designing novel materials and drugs.

Purpose of the Study:

• To experimentally and computationally compare the relative strengths of S-π and O-π interactions.
• To elucidate the factors governing the stability switch between S-π and O-π interactions.

Main Methods:

• Conducted a comprehensive experimental survey using 36 molecular balances.
• Compared 18 pairs of S-π versus O-π interactions across diverse structural, geometric, and solvent parameters.
• Employed computational studies of bimolecular complexes (PhSCH3-arene and PhOCH3-arene) to validate experimental findings.

Main Results:

• Observed a strong linear correlation between folding energies of sulfur and oxygen balances.
• Demonstrated a systematic switch in stability from O-π to S-π interactions.
• Computational studies successfully replicated the experimental trends.

Conclusions:

• The stability of S-π interactions is generally greater than O-π interactions.
• The observed preference shift is attributed to the interplay of stabilizing (dispersion, solvophobic) and destabilizing (exchange-repulsion) terms.
• Differences in atomic size and polarizability between oxygen and sulfur are critical factors.