Supramolecular Similarity in Polymorphs: Use of Similarity Indices (IX)

A systematic investigation to assess the degree of similarity between polymorphs was carried out. A similarity indices (I-X) approach was applied in ten series of polymorphs with different characteristics and number of molecules in the asymmetric unit. Geometric (I-D), contact area (I-C), and stabilization energy (I-G) parameters were used. It was possible to situate each comparison in different regions of similarity within the polymorphism phenomenon and determine the boundaries between quasi-isostructural polymorphs and polymorphs of low similarity. The multiparameter I-DCG index was used as a robust tool to determine the total similarity within the polymorphism phenomenon. The highest contribution of the stabilization energy parameter (45%) toward the final value of similarity (I-DCG) was observed, followed by the contact area index (32%). The geometric index contributed approximately 23% to the final value of I-DCG. This information reinforces the importance of the contact area and stabilization energy in assessing the degree of similarity between crystalline structures. A new descriptor (I-Q) based on the comparison of the energetic contribution of intermolecular interaction types present in each crystal structure is presented. I-Q can be a versatile tool and applicable even for systems that do not share any similarity.