Diazole-based powdered cocrystal featuring a helical hydrogen-bonded network: structure determination from PXRD,...

Area of Science:

• Crystal engineering
• Supramolecular chemistry
• Solid-state chemistry

Background:

• Cocrystals are crystalline solids composed of two or more molecular components.
• Azoles, such as pyrazoles and imidazoles, are important heterocyclic compounds with diverse applications.
• Understanding intermolecular interactions is crucial for designing novel crystalline materials.

Purpose of the Study:

• To synthesize and characterize a new equimolar cocrystal of 3,5-dimethyl-1H-pyrazole (dmpz) and 4,5-dimethyl-1H-imidazole (dmim).
• To elucidate the structural features, including hydrogen bonding and weak interactions, that stabilize the cocrystal.
• To investigate the effect of molecular structure on cocrystal formation and network topology.

Main Methods:

• Powder X-ray diffraction (PXRD) for crystal structure determination.
• High-resolution solid-state Nuclear Magnetic Resonance (NMR) spectroscopy (1D/2D 13C, 15N, 1H) for local structural insights.
• Molecular modeling and Density Functional Theory (DFT) calculations for structure refinement and analysis.
• Synthesis of various imidazole derivatives to study methylation effects.

Main Results:

• A novel 1:1 cocrystal (dmpz···dmim) was successfully synthesized and its structure determined.
• The cocrystal exhibits an atypical 1D helicoidal hydrogen-bonded network, resembling alpha-helix structures in proteins.
• NH···N hydrogen bonds and CH···π contacts were identified as key stabilizing interactions.
• DFT refinement significantly improved the structural model derived from PXRD data.
• Only 4,5-dimethyl-1H-imidazole among tested derivatives formed a cocrystal with dmpz, highlighting the role of substituent placement.

Conclusions:

• The dmpz···dmim cocrystal represents the first example of a cocrystal formed between two different azoles.
• The study demonstrates the successful rational design of cocrystals with specific network topologies through control of intermolecular interactions.
• The findings provide valuable insights into the self-assembly principles governing the formation of complex supramolecular structures.