Systematic design strategies to achieve ternary cocrystals

Targeted synthesis of ternary cocrystals can be achieved by size and shape mimicry, i.e. replacing molecules in crystal lattice with molecules of similar size and shape. Further an intermolecular interaction within a structure can be substituted by another intermolecular interaction with different geometric and energetic functions with little change in structural packing, i.e. interaction mimicry.


Recently three ternary co-crystals of 4,4′-bis-hydroxyazobenzene have been 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.


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  2. Tothadi, S, Desiraju, GR. Chem. Commun. 2013, 49, 7791-7793.