Concomitant cocrystal and salt: no interconversion in the solid state.

Area of Science:

• Crystallography
• Materials Science
• Chemical Engineering

Background:

• Investigating the solid-state behavior of molecular salts and cocrystals is crucial for understanding their stability and potential applications.
• Beta-alanine and DL-tartaric acid form both a molecular salt and a cocrystal with identical chemical formulas but distinct structures.
• Previous research indicated a solvent-mediated phase transition between the salt and cocrystal forms in a slurry.

Purpose of the Study:

• To examine the thermal stability and phase behavior of the beta-alanine and DL-tartaric acid molecular salt and cocrystal.
• To determine if interconversion or polymorphic transitions occur between the two solid forms over a wide temperature range.
• To compare the observed thermal behavior with previously reported solvent-mediated transitions.

Main Methods:

• Single-crystal X-ray diffraction was employed to analyze the crystal structures.
• Powder X-ray diffraction was utilized to study phase identification and transitions.
• Variable temperature studies were conducted from 100 K up to the melting points of the compounds.

Main Results:

• Both the molecular salt and the cocrystal of beta-alanine and DL-tartaric acid were stable over the studied temperature range.
• No evidence of interconversion between the salt and cocrystal phases was found.
• No polymorphic transitions were detected for either the salt or the cocrystal within the experimental temperature limits.

Conclusions:

• The molecular salt and cocrystal of beta-alanine and DL-tartaric acid exhibit distinct solid-state behaviors.
• Unlike solvent-mediated transitions, thermal treatment does not induce interconversion between these two forms.
• The findings highlight the importance of considering the specific conditions (e.g., solvent presence) when predicting phase transformations in crystalline materials.