Arylethynyl Helices Supported by π-Stacking and Halogen Bonding.

Area of Science:

• Crystal Engineering
• Supramolecular Chemistry
• Organic Materials

Background:

• Arylethynyl (AE) molecules are versatile building blocks in supramolecular chemistry.
• Halogen bonding and pi-pi stacking are key non-covalent interactions driving self-assembly.
• Controlling helical structures in the solid state remains a significant challenge.

Purpose of the Study:

• To investigate the co-crystallization of a pyridyl-containing arylethynyl (AE) moiety with 1,4-diiodotetrafluorobenzene.
• To elucidate the driving forces behind the formation of unique helical motifs.
• To understand the interplay between halogen bonding and pi-pi stacking in crystal assembly.

Main Methods:

• Co-crystallization experiments.
• Single-crystal X-ray diffraction analysis.
• Computational calculations (e.g., DFT) to quantify interaction energies.

Main Results:

• Formation of figure-eight shaped helical motifs in the crystal lattice.
• Interspersion of left-handed (M) and right-handed (P) helices in a regular pattern.
• Identification of halogen bonding (N⋅⋅⋅I, 2.81–2.84 Å) and pi-pi stacking (3.57 Å) as primary assembly forces.
• Evidence of mutual enhancement between halogen bonding and pi-pi stacking interactions.

Conclusions:

• The co-crystallization strategy successfully yielded complex helical architectures.
• Synergistic halogen bonding and pi-pi stacking interactions are crucial for the observed self-assembly.
• This study provides insights into designing ordered supramolecular structures through non-covalent interactions.