On the Influence of Solvent Properties on the Structural Characteristics of Molecular Crystal Polymorphs

A set of structures of homomolecular organic crystals with information on the solvent utilized for crystallization was extracted from the Cambridge Structural Database in order to identify possible general relationships between changes in the crystal structure characteristics of polymorphs and changes in the properties of solvents from which they were crystallized. Feature descriptions of crystal structures and solvents were introduced, which are based on various types of numerical descriptors reflecting different aspects of crystal structures (molecular packing characteristics, lattice energy) and solvent properties (polarity, acid–base behavior, bulk characteristics, etc.). A statistical analysis of the studied set of compounds revealed that the crystal structures of polymorphs obtained from different solvents tend to differ slightly more from each other than the crystal structures of polymorphs crystallized from the same solvent, though these differences in crystal structure properties are not statistically significant. By analyzing the subset of polymorphs obtained from different solvents, we have discovered positive correlations between changes in the tightness of molecular packing and the solvent’s descriptors related to polarity (Spearman’s correlation coefficients ρ = 0.28–0.33). Notably, the more similar the molecular conformations in crystals of polymorphs and the more polar the compound, the more pronounced are the identified correlations (moderate correlations with ρ = 0.5–0.6). At the same time, the expected correlations between changes in the conformation-related properties of a molecule in a crystal and changes in the solvent properties were not found.