Controlling polymorphism in molecular cocrystals by variable temperature ball milling.

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• Mechanochemistry offers unique pathways for solid form modification, distinct from solution-based methods.
• Controlling solid-state polymorphism via mechanochemistry remains underexplored, necessitating dedicated research.
• Understanding mechanochemical transformations is crucial for novel material design.

Purpose of the Study:

• To investigate the induction of polymorphism in molecular solids using mechanochemical techniques.
• To compare mechanochemically induced solid-state transitions with conventional thermal methods.
• To explore the influence of mechanochemistry on energy barriers for polymorphic transitions.

Main Methods:

• Utilized ball milling as a mechanochemical technique.
• Employed a model organic cocrystal system: isonicotinamide:glutaric acid.
• Investigated solid-state transitions at varying temperatures under milling conditions.

Main Results:

• Demonstrated mechanochemical induction of polymorphism in the model cocrystal system.
• Achieved a solid-form transition (Form II to Form I) at a lower temperature (348 K) via ball milling compared to thermal transition (363 K).
• Mechanochemical processing significantly reduced the energy required for the solid-state transition.

Conclusions:

• Mechanochemistry provides a viable route to control polymorphism and induce solid-state transitions under milder conditions.
• Mechanochemical techniques can lower the energy barriers for solid form interconversion.
• Interpreting mechanochemical solid-form landscapes may require novel approaches beyond equilibrium-based models.