Structural Diversity of Ethinyl Estradiol Solvates

The (pseudo)polymorphism of ethinyl estradiol was investigated via extensive crystallization experiments. Four new crystal structures of ethinyl estradiol solvates that resulted from this study are presented. They contain dioxane, nitromethane, ethanol, or dimethylformamide. The crystal structures of the hemihydrate, methanolate, and acetonitrile solvate were redetermined to obtain the accurate hydrogen atom positions. The structural details of the different solvates of ethinyl estradiol were investigated in order to understand the scope of the solvate formation of ethinyl estradiol. Ethinyl estradiol forms many solvates, mostly with solvents having H-bond accepting or both accepting and donating propensity. Despite our rather comprehensive study, no true polymorph of ethinyl estradiol anhydrate was found.