Abstract
During the solution-mediated crystallization of N-(3-ethynylphenyl)-3-fluorobenzamide, small variation in the process conditions can lead to two new polymorphic forms in addition to the three previously reported forms. Structural features of the two new forms and mechanical properties of the three stable polymorphs, among the five forms, have been investigated using instrumented nanoindentation. The results show that among the three stable forms (Form I, Form II, and Form III) of the compound, the Form II crystal exhibits the lowest hardness (H) and elastic modulus (E), while these values are nearly similar for Form I and Form III crystals. Interestingly, the direct correlation of mechanical properties with the density of crystals was found for three polymorphs, but their melting points do not follow similar trends. The quantitative analysis of structural features with the inputs from energy frameworks suggests that the anisotropy in mechanical properties of the three polymorphs originate from the different orientations of strong to moderate N-H⋯O hydrogen bonds and weak to strong π⋯π stacking interactions, which mainly stabilize the crystal packing of the three polymorphs.
