Co-Crystallization Kinetics of 2:1 Benzoic Acid-Sodium Benzoate Co-Crystal: The Effect of Templating Molecules in a Solution

The addition of dissolved templating molecules in crystallization will create supramolecular assemblies within the solution, serving as anchor points for the solute molecules to nucleate and grow. In this work, nucleation and crystal growth kinetics of 2:1 benzoic acid (HBz)-sodium benzoate (NaBz) co-crystallization with or without templates in a solution were analyzed by monitoring the concentration of the mother liquor during cooling crystallization. The results showed that the addition of the dissolved 2:1 or 1:1 HBz-NaBz co-crystals as templating molecules could reduce the critical free energy barrier of 2:1 HBz-NaBz co-crystal during its nucleation, but did not significantly affect the order of crystal growth rate. On the other hand, the critical free energy barrier of the nucleation process was increased if dissolved NaBz was used as a templating molecule, while a significant rise in the order of crystal growth rate occurred. The crystal habit obtained from the NaBz-templated system was needle-like, suggesting that sodium-sodium coordination chains of NaBz supramolecular assemblies in the solution phase were responsible for creating elongated crystals. Conversely, a large prismatic crystal habit found in non-templated and 2:1 and 1:1 HBz-NaBz co-crystal-templated systems implied that those templating molecules formed sparsely interconnected supramolecular assemblies in the solution phase.

Automated summary

The study analyzed the nucleation and crystal growth kinetics of 2:1 HBz-NaBz co-crystals with or without templates by monitoring the concentration of the mother liquor. The results showed that adding dissolved templating molecules could reduce the critical free energy barrier of nucleation for the co-crystals, while the crystal growth rate was not significantly affected. Additionally, the type of templating molecule used influenced both the critical free energy barrier of nucleation and the order of crystal growth rate.