Intermolecular π-π Stacking Interactions Made Visible

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Chemical Education

Background:

• Noncovalent intermolecular interactions, particularly π-π stacking, are fundamental to molecular assembly and material properties.
• Visual demonstrations of these interactions are valuable for understanding chemical principles.
• Hexafluorobenzene and mesitylene are common aromatic compounds.

Purpose of the Study:

• To demonstrate the existence and effect of π-π stacking interactions through a simple, visual experiment.
• To explore the formation of crystalline solids from mixtures of aromatic liquids.
• To provide an accessible and cost-effective experiment for educational purposes.

Main Methods:

• Mixing hexafluorobenzene (1) and 1,3,5-trimethylbenzene (mesitylene, 2) in various volume ratios.
• Observing the formation of a crystalline solid and measuring its melting point.
• Testing other liquid aromatic compounds as substitutes for mesitylene.

Main Results:

• Mixing hexafluorobenzene and mesitylene yields a crystalline solid with a melting point of 34 °C.
• The solid structure features alternating, π-π stacked pillars of both aromatic molecules.
• Mixtures within a broad range of volume (2/3 to 3/2) and molar (1.8–0.8) ratios produced similar visual results.
• Crystalline solid formation was also observed with o-xylene, p-xylene, and aniline, but not with many other tested aromatics.

Conclusions:

• The experiment provides a clear visual demonstration of π-π stacking interactions.
• The formation of crystalline solids from these mixtures is robust and visually apparent.
• This simple experiment is suitable for educational settings due to its low cost, speed, and safety.