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Ordered and Plastic Crystals in the Complex Polymorphism of Pinanediol
Authors: Joana F. C. Silva; Mario T. S. Rosado; Malgorzata Jasiurkowska Delaporte; Manuela Ramos Silva; M. Fatima M. Piedade; Ewa Dryzek; M. Ermelinda S. Eusebio
Ref.: Cryst. Growth Des. 19, 6127-6135 (2019)
Abstract: Plastic crystals, frequently observed for compounds with globular molecules, are mesophases characterized by orientational disorder maintaining positional order. The present work focuses on finding correlations between the plastic crystal formation ability of pinanediol, its molecular shape, and the intermolecular interactions existing in solid phases. Pinanediol, a bicyclical monoterpenoid and vicinal diol, is a globular molecule capable of forming intermolecular hydrogen bonds. In the present work, the structure and thermal behavior of this compound in the solid state is studied for the first time. Despite its strong intermolecular interactions in condensed phases, it was found to be a plastic crystal former showing complex polymorphism. Three ordered phases were identified by differential scanning calorimetry, polarized light thermal microscopy, and X-ray diffraction with variable temperature. The molecular dynamics in different polymorphic forms was studied by broadband dielectric spectroscopy (BDS). The structure of the most stable enantiopure ordered polymorph of pinanediol was resolved by single-crystal X-ray diffraction, using crystals of both enantiomers. Its intermolecular close contacts were studied by Hirshfeld surface analysis, which was used to determine shape parameters correlated to plastic crystal formation ability. It was concluded that the globular shape of pinanediol allows the formation of the plastic phase that is not inhibited by the presence of intermolecular hydrogen bonding.
