Stacking Interactions: A Supramolecular Approach to Upgrade Weak Halogen Bond Donors

Area of Science:

• Crystal Engineering
• Supramolecular Chemistry
• Halogen Bonding

Background:

• Tetracyanobenzene (TCB) is a versatile building block in crystal engineering.
• Haloarenes are known to participate in halogen bonding (HaB).
• Understanding non-covalent interactions is crucial for designing functional materials.

Purpose of the Study:

• To synthesize and characterize new co-crystals of TCB with various haloarenes.
• To investigate the role of π⋅⋅⋅π stacking and σ-hole interactions in enhancing halogen bonding.
• To theoretically elucidate the factors governing the strength of X⋅⋅⋅N_cyano halogen bonds.

Main Methods:

• Co-crystallization of TCB with six different haloarenes.
• X-ray diffraction analysis of the resulting co-crystals.
• Density Functional Theory (DFT) calculations and molecular electrostatic potential mapping.

Main Results:

• Six new co-crystals of TCB⋅⋅⋅ArX were successfully synthesized and characterized.
• Strong collective effects of π⋅⋅⋅π stacking and lone pair-(X)⋅⋅⋅π-hole-(C) interactions were observed.
• Theoretical studies revealed that stacking interactions significantly increase the σ-hole depth of haloarenes, boosting their HaB donor ability.
• A dramatic increase in X⋅⋅⋅N_cyano HaB strength was demonstrated for stacked trimers compared to unstacked haloarenes.

Conclusions:

• Co-crystallization with TCB effectively enhances halogen bonding in haloarenes via synergistic non-covalent interactions.
• π⋅⋅⋅π stacking plays a critical role in modulating the electronic properties of haloarenes, thereby strengthening their halogen bonding capabilities.
• The findings provide valuable insights into the rational design of supramolecular assemblies with tunable halogen bonding interactions.