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

Freshsya Zata Lini,Dhanang Edy Pratama,Tu Lee

doi:10.3390/cryst11070812

Freshsya Zata Lini, Dhanang Edy Pratama + Show 1 more

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https://doi.org/10.3390/cryst11070812

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Journal: Crystals	Publication Date: Jul 12, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: National Central University

Abstract

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.

Highlights

Co-crystallization is one of the available techniques to alter the physicochemical properties of a molecule, where a molecule is paired with a suitable non-volatile molecule called co-former
The addition of sodium-rich NaBz templating molecules could slightly increase the interfacial energy γ, critical free energy ∆Gcrit, critical nucleus radius rcrit, and the number of molecules in the critical nucleus i* due to the rearrangement of the coordination complexes of sodium with another sodium atom and carboxylate ligand within the supramolecular assemblies of the template to accommodate both sodium–carboxylic coordination and carboxylic–carboxylate hydrogen bonding moiety. The differences in those thermodynamic parameters among a non-templated system and 2:1 and 1:1 HBz–NaBz co-crystal templating molecules were negligible because the intermolecular interactions of the supramolecular assemblies of the template and the solute molecules were similar with each other
The order of the crystal growth kinetics of 2:1 HBz–NaBz co-crystals depended on S0 for the non-templated and NaBz-templated co-crystallization

Summary

Introduction

Co-crystallization is one of the available techniques to alter the physicochemical properties of a molecule, where a molecule is paired with a suitable non-volatile molecule called co-former. These molecules are paired with each other in a stoichiometric ratio and form a crystal with distinct lattice parameters, differing it with solid solution. This pairing is facilitated by intermolecular hydrogen bonds, π–π interaction, halogen bonds, and Van der Waals forces, without any proton transfer, an important feature distinguishing it with salt formation reaction [1]. Co-crystallization is gaining importance outside pharmaceutical field, with some of its applications in reducing the hygroscopicity of fertilizer [9] and improving the stability of an explosive agent [10]

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