Hydrogen bonding vs. halogen bonding: the solvent decides

Area of Science:

• Supramolecular Chemistry
• Crystallography
• Materials Science

Background:

• Controlling intermolecular interactions is key to understanding and utilizing self-assembly processes.
• Hydrogen bonds and halogen bonds are fundamental directional intermolecular forces with distinct properties.
• Co-crystal formation offers a route to engineer materials with desired properties.

Purpose of the Study:

• To investigate the role of solvent polarity in directing the competitive self-assembly of co-crystals.
• To determine how solvent choice influences the dominance of hydrogen bonds versus halogen bonds in co-crystal formation.
• To explore the relationship between solvent effects and the relative strengths of competing intermolecular interactions.

Main Methods:

• Investigated competitive co-crystal formation using three pairs of hydrogen bond and halogen bond donors with a common acceptor.
• Examined co-crystal formation in seven different solvents with varying polarities.
• Analyzed product formation and phase purity using powder X-ray diffraction (PXRD).

Main Results:

• Hydrogen-bonded co-crystals were favored in less polar solvents.
• Halogen-bonded co-crystals were favored in more polar solvents.
• The switch in dominance from hydrogen to halogen bonds was dependent on relative interaction strengths and solvent polarity.

Conclusions:

• Solvent polarity is a critical factor in controlling the self-assembly of co-crystals through competitive intermolecular interactions.
• Understanding solvent effects is essential for precisely directing co-crystal formation and harnessing self-assembly.
• The findings provide a framework for designing and synthesizing co-crystals with predictable structures and properties.