Relationship between the Crystal Structure and Morphology of Carboxylic Acid Polymorphs. Predicted and Experimental Morphologies

Polymorphs of carboxylic acids crystallize from solvent evaporation experiments as crystals with needle or plate morphology. Experimentally, it has been observed that the crystallization solvent does not sensibly modify the crystal morphology of a given polymorph. Hence, a theoretical study of the morphology of these polymorphs was conducted to relate the crystal structures with their macroscopic crystal shapes. Methodologies with an increasing degree of complexity were used, and the best results were obtained from those calculations considering the attachment energy ( E att hkl ) released on attachment of a new d hkl layer to a growing crystal surface. The experimental habits of the polymorphs of carboxylic acids are reproduced well by the morphology simulations, so the observed crystal shapes can be rationalized in terms of the intermolecular interactions between the growth units. In the crystal structures of the C, B, and E polymorphs, layers of pure CH 3 residues produce weak van der Waals interactions resulting in strongly anisotropic crystal growth (platy crystals) with highly developed {100} faces.