Abstract
Two polymorphic forms of a conformationally flexible molecule, 5-[(Diphenylphosphoryl)methyl]-4-(prop-2-en-1-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione, were obtained by crystallization and characterized by X-ray diffraction analysis and differential scanning calorimetry. The relative stability of polymorphic forms was estimated with DFT calculations of crystal structures and isolated molecules. It turns out, that in the first more dense polymorph with higher cohesion energy and crystal lattice energy, the molecule adopts an energetically unfavorable conformation, and forms dimers with lower H-bond strength, as compared to the second polymorph. On the other hand, in the second polymorph, the molecule adopts almost the lowest-energy conformation and forms infinite chains via strong H-bonds. The first form that seems to be more thermodynamically stable at room temperature transforms into the second form via two endothermic phase transitions; the apparent irreversibility of the transition is due to high energy difference between the molecular conformations in crystals.
Highlights
Despite many years of research, the polymorphism of molecular crystals remains one of the most fascinating and important phenomena in materials science [1]
For biologically active compounds used as active pharmaceutical ingredients (API), the identification and characterization of polymorphic forms is of particular importance [3]
Ab initio calculations of crystal structures and their isolated associates were performed with CRYSTAL17 software package [26], commonly used for the density functional theory (DFT) modeling of solid-state 3D structures, and capable for calculations of 0D and
Summary
Despite many years of research, the polymorphism of molecular crystals remains one of the most fascinating and important phenomena in materials science [1]. Another responsible the stabilize enhanced probability of polymorphism, in crystal can, infactor principle, not onlyfor nearly isoenergetic conformations, but alsois the for mation of different synthons. Structural unit within supermolecules which can be formed and/or assembled by known or conceiv Another factor responsible for the enhanced probability of polymorphism, is the formation of different supramolecular synthons. Supramolecular synthon defined able synthetic operations involving intermolecular [7] and is one of theasmost im “a structural unit within supermolecules which can be formed and/or assembled by known or portant and fruitful concepts in crystal engineering directly related to polymorphism.
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