Co-Crystallization Thermodynamics of Two-Component Crystals: Databases, Polymorphism, and Stoichiometry Differences

Based on the literature analysis, we have built up a database containing fusion temperatures and enthalpies of two-component molecular cocrystals and individual compounds (3032 occurrences). The overall database was divided into several smaller databases, each of which comprised the two-component systems used as functional materials in a specific industrial sector. Comparative analysis of the mentioned databases has been done. Formation thermodynamics of the two-component crystals have been evaluated. A new algorithm for estimating the sublimation Gibbs energies of molecular crystals based on clustering of the database has been developed. Using this approach, we have evaluated and analyzed the thermodynamic formation functions for 1005 two-component crystals from the total database of 3032. A number of the correctly predicted systems were shown to be 73.6% of all the systems described in the literature. Co-crystallization processes were entropy-determinated for 23% of the two-component systems. Thermodynamic functions of polymorphic phase transitions for 95 pairs were evaluated. For 78 pairs, the considered phase transitions were shown to be monotropic, whereas for 17 (18% of 95) pairs, they were enantiotropic. The criteria for splitting the polymorphic forms into these groups are presented. In this study, 44 systems with the same composition and different stoichiometries (with fully calculated formation thermodynamic functions) were analyzed. A substance with the highest melting point was selected as the first component of a two-component crystal. Based on this, we adjusted the stoichiometry. As a result, four groups of two-component crystals were obtained. It was shown that the formation Gibbs energies of the two-component crystals with a given stoichiometry and with a higher melting point were lower as compared to the similar crystals with different stoichiometric compositions (more thermodynamically stable).