Polymorphs of N-[2-(Hydroxymethyl)phenyl]benzamide: Structural Characterization and Analysis of Molecule···Molecule Interactions by Means of Atom−Atom Potentials and DFT

Two polymorphs of N-[2-(hydroxymethyl)phenyl]benzamide have been identified and their structures elucidated. Both crystallize in P21/n but with different unit cell parameters and crystal packing. The less stable polymorph II undergoes a first order phase transition to polymorph I at 85 °C, as determined using variable temperature powder diffraction studies. The arrangement of molecules in both structures is characterized by intramolecular ring-forming N−H···O(H) and chain-forming intermolecular O−H···OC hydrogen bonds. It is, however, the nature of the dispersive interactions due to π overlap that differentiates the two structures. In polymorph I, these exist in a molecule···molecule interaction that also accommodates the O−H···OC hydrogen bond. Calculations using atom−atom potential methods, and corroborated using DFT methods, indicate that the interaction energy of this pair of molecules accounts for at least half of the total lattice energy of the structure. Carrying out the equivalent calculations on polymorph II shows that the dispersive interactions due to π overlap and the O−H···OC hydrogen bond are separated into two different molecule···molecule interactions. This suggests that determining the distinctive interactions between pairs of molecules may provide some insight into how to inhibit them and, hence, favor the growth of other crystal forms.