Ferrocene-Containing Pseudorotaxanes in Crystals: Aromatic Interactions with Hammett Correlation

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Organic Chemistry

Background:

• Pseudorotaxanes are supramolecular assemblies with potential applications in molecular machines and materials science.
• Understanding non-covalent interactions, such as pi-pi stacking, is crucial for designing and controlling these structures.
• Ferrocene derivatives and crown ethers are common components in the construction of rotaxanes and pseudorotaxanes.

Purpose of the Study:

• To synthesize and characterize novel pseudorotaxane single crystals.
• To investigate the structural features and intermolecular interactions within these pseudorotaxanes.
• To explore the relationship between the electronic properties of substituents and the observed crystal structures.

Main Methods:

• Synthesis of ferrocenylmethyl(arylmethyl)ammonium and dibenzo[24]crown-8 (DB24C8) macrocycles.
• Crystallization of pseudorotaxanes from solution.
• X-ray crystallographic analysis to determine precise molecular structures and orientations.

Main Results:

• Single crystals of pseudorotaxanes incorporating various aryl-substituted ferrocenylmethylammonium axles and DB24C8 macrocycles were successfully obtained.
• X-ray diffraction revealed close centroid distances and parallel or tilted orientations between the aryl ring of the axle and the catechol ring of the macrocycle.
• A correlation was observed between the centroid distances in structures with parallel aromatic rings and the Hammett substituent constants of the aryl groups.

Conclusions:

• The study demonstrates the successful formation and structural elucidation of novel ferrocene-based pseudorotaxanes.
• The findings highlight the importance of pi-pi interactions in dictating the self-assembly and structural organization of these supramolecular systems.
• The quantitative relationship between substituent effects and structural parameters provides valuable insights for the rational design of related supramolecular architectures.