Crystalline Solid Forms of Rufigallol

Simple hydroxy-substituted 9,10-anthraquinones form a small family of compounds with a remarkably large number of uses. Although the compounds are often employed in solid form, few structures have been reported to show how crystallization is controlled by factors such as an extended planar topology and the potential to engage in hydrogen bonding and charge-transfer interactions. The paucity of structural data creates an obstacle to understanding the behavior of hydroxyanthraquinones in the solid state. To provide additional information, we have studied 1,2,3,5,6,7-hexahydroxy-9,10-anthraquinone (rufigallol) and determined the structures of an anhydrous form, two dihydrates, and other solvates. Comparing these structures with those of other hydroxyanthraquinones reveals certain shared features as well as preferences of rufigallol not shown by anthraquinones with fewer OH groups. Our results create a foundation for discovering advanced materials derived from highly hydroxylated anthraquinones and related compounds.