Influence of Solvent Composition on the Crystal Morphology and Structure of p-Aminobenzoic Acid Crystallized from Mixed Ethanol and Nitromethane Solutions

Research output: Contribution to journalArticle

  • External authors:
  • I. Rosbottom
  • C. Y. Ma
  • T. D. Turner
  • R. A. O'Connell
  • Jonathan J. Loughrey
  • Ghazala Sadiq
  • K. J. Roberts


The crystallization of α-p-aminobenzoic acid (pABA) from mixed solutions in ethanol (EtOH) and nitromethane (NMe) is reported. From solutions with compositions >60 wt % NMe, the known α-polymorph of pABA appears. In contrast, crystals prepared from mixed solvent with <60 wt % NMe reveal the presence of a previously unknown NMe solvate, which crystallizes concomitantly with the α-form. The crystal structure of this new form has been determined and is compared with the previously known structure of the α-polymorph. The crystal structure of the NMe solvate has similar synthonic interactions with respect to α-pABA, in particular, the OH···O H-bonded dimers and the NH···O H-bonds between the pABA molecules. However, the π-π stacking interactions between the phenyl ring groups are found to be much more offset and do not form a continuous chain through the structure, as found in α-pABA. The synthonic interactions in the NMe solvate structure are generally weaker than those found in α-pABA, and the lattice energy is calculated to be significantly lower, suggesting the solvate structure is metastable with respect to α-pABA. The impact of NMe on the morphology of α-pABA crystals, together with molecular modelling results suggest that this solvent is able to disrupt the π-π stacking interactions that dominate growth along the needle (b-axis) direction of α-pABA, and are intimately linked to the ultimate formation of the solvate.

Bibliographical metadata

Original languageEnglish
Pages (from-to)4151-4161
Number of pages11
JournalCrystal Growth and Design
Issue number8
Early online date27 Jun 2017
Publication statusPublished - 2 Aug 2017

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