Halogen Bonding Involving Isomeric Isocyanide/Nitrile Groups.

Area of Science:

• Crystal Engineering
• Supramolecular Chemistry
• Halogen Bonding

Background:

• Halogen bonds (HaBs) are crucial noncovalent interactions in crystal engineering.
• Understanding the interplay between isocyanide and nitrile groups in HaBs is essential for designing novel materials.

Purpose of the Study:

• To investigate the formation and characteristics of cocrystals involving diisocyanides, dinitriles, and a halogen bond donor.
• To compare the halogen bonding interactions of isocyanide versus nitrile groups within isostructural crystal environments.
• To elucidate the nature and contributing forces of the observed halogen bonds through theoretical analysis.

Main Methods:

• Co-crystallization of 2,3,5,6-tetramethyl-1,4-diisocyanobenzene, 1,4-diisocyanobenzene, and 1,4-dicyanobenzene with 1,3,5-triiodotrifluorobenzene.
• X-ray diffraction analysis of the resulting cocrystals.
• Computational chemistry methods to study the electronic structure and bonding interactions.

Main Results:

• Three cocrystals were successfully synthesized and characterized: 1·1,3,5-FIB, 2·2(1,3,5-FIB), and 3·2(1,3,5-FIB).
• A common feature is the presence of I···C_isocyanide or I···N_nitrile halogen bonds.
• Diisocyanide cocrystals exhibited stronger binding and higher nucleophilicity compared to dinitrile cocrystals.
• Electrostatic interactions dominate the HaBs, with significant contributions from dispersion and induction forces.

Conclusions:

• The study provides a direct comparison of halogen bonding involving isocyanide and nitrile functionalities in similar crystal structures.
• Diisocyanides are confirmed to be stronger halogen bond acceptors than dinitriles.
• The findings contribute to a deeper understanding of halogen bonding principles for rational crystal design.