Predicting and understanding crystal morphology: the morphology of benzoic acid and the polymorphs of sulfathiazole

Abstract

Crystals of benzoic acid grown from dichloromethane and acetonitrile are greatly extended along the b-axis. The enhanced growth is not related to hydrogen bonding as benzoic acid is respectively dimeric and monomeric in these solvents. A mechanism is suggested for enhanced growth in the π-stacking direction for flat π-stacking systems. Facilities have been added to the Oscail software package which provide attachment energy calculations, crystal surface analysis and crystal visualization. Crystal surface analysis can be used to find the π-stacking direction and to identify the density of available hydrogen bond donors and acceptors on crystal faces. Observed and calculated morphologies for crystals of sulfathiazole form 2 grown from ethanol are in good agreement. Differences in the observed and calculated shapes of sulfathiazole forms 1, 3, 4 and 5 are attributed to solvent effects which correlate with the density of available hydrogen bond acceptors on crystal faces.