Establishing Halogen‐Bond Preferences in Molecules with Multiple Acceptor Sites

The interplay between hydrogen bonds (HBs) and halogen bonds (XBs), has been addressed by co‐crystallizing two halogen bond donors, 1,4‐diiodotetrafluorbenzene(DITFB) and 1,3,5‐trifluoro‐2,4,6‐triiodobenzene(TITFB) with four series of targets; N‐(pyridin‐2‐yl)benzamide (Bz‐X), N‐(pyridin‐2‐yl)picolinamides (2Pyr‐X), N‐(pyridin‐2‐yl)nicotinamides (3Pyr‐X), N‐(pyridin‐2‐yl)isonicotinamides (4Pyr‐X); X=H/Cl/Br/I. The structural outcomes were compared with interactions in the targets themselves. 13 co‐crystals were analysed by single‐crystal X‐ray diffraction (SCXRD). In all three co‐crystals from the 2Pyr series, the intramolecular HB remained intact while the XB donors engaged with the N(pyr) or O=C sites. In the ten co‐crystals from the other three series, the intermolecular HBs present in the individual targets were disrupted in 9/10 cases. Overall, the acceptor sites selected by the halogen‐bond donors in these targets were distributed as follows; N(pyr)=81 %, O=C (15 %) or π (4 %). A series of co‐crystallization experiments with halogen bond donors and sixteen target molecules was carried out to map preferred binding sites of halogen‐bond donors, and it was found to be in the order of π (4 %)