Designing Ternary Co-crystals with Stacking Interactions and Weak Hydrogen Bonds. 4,4′-Bis-hydroxyazobenzene

Three ternary co-crystals of the title compound are reported. The design strategy hinges on the identification of a robust synthon with O–H···N hydrogen bonds in a binary co-crystal. Construction of this module allows the tuning of π···π stacking interactions and weak hydrogen bonds to incorporate the third component into the crystal structure. Screening of various co-formers showed that a delicate balance of electrostatics is required for stacking to favor the formation of ternaries. A C–H···N hydrogen-bonded motif was also found to occur repetitively in the ternary co-crystals. The directional nature of weak hydrogen bonds allows them to be used effectively in this study.