Impact of Hydrogen and Halogen Bonding Interactions on the Packing and Ionicity of Charge-Transfer Cocrystals

With an aim of understanding the influence of robust charge-transfer (CT) interactions and auxiliary hydrogen and halogen bonds in tailoring the crystal packing, we have synthesized four CT cocrystals involving 1,5-diaminonaphthalene (DAN) as the donor and fluoranil (FA), chloranil (CA), bromanil (BA), and iodanil (IA) as acceptors. While the CT interactions take the primary role in guiding the three-dimensional assembly in all the cocrystals, N–H···O and C–H···O hydrogen bonds play a significant role as auxiliary interactions in stabilizing the mixed stack arrangement in DAN–FA, DAN–CA, and DAN–BA cocrystals, whereas I···N halogen bonds assist the segregated stack supramolecular packing in DAN–IA. The experimentally determined ionicity values of mixed stack DAN–CA and DAN–BA cocrystals were found to be 0.27 and 0.23 e, indicating significant CT that increases with electronegativity of the halogen substituents.