The effect of mechanical interlocking on crystal packing: predictions and testing

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Crystallography

Background:

• Mechanically interlocked molecular architectures, such as rotaxanes, offer potential for solid-state devices.
• Understanding molecular mobility within crystalline phases is crucial for their application.

Purpose of the Study:

• To predict and test the solid-state mobility of benzylic amide macrocycle-containing rotaxanes.
• To identify rotaxane structures suitable for molecular-level mechanical motion in the solid state.

Main Methods:

• Statistical analysis of X-ray crystal structures.
• Molecular mechanics-based solid-state calculations.
• Atomic force microscopy (AFM) experiments.

Main Results:

• Crystal packing of rotaxanes shows similarities and differences with non-interlocked molecules.
• Principal component analysis (PCA) identified key factors (size, packing, stoichiometry, H-bonding) influencing crystal properties.
• AFM experiments confirmed rotaxanes can exhibit significant solid-state mobility, contrary to initial intuition.

Conclusions:

• Intramolecular hydrogen bonding saturation influences crystal assembly.
• Macrocycle-crystal environment interactions are critical for mobility.
• Guidelines are proposed for designing rotaxanes with mobile components for solid-state applications.