Role of secondary interactions in a series of 2:1 halogen‐bonded cocrystals formed between 4‐(dimethylamino)pyridine and ditopic halogen‐bond donors

The structures of a series of 2:1 cocrystals formed between 4‐(dimethylamino)pyridine and each of 1,2,4,5‐tetrachloro‐3,6‐diiodobenzene, 2C7H10N2·C6Cl4I2, 1,2,4,5‐tetrabromo‐3,6‐diiodobenzene, 2C7H10N2·C6Br4I2, 1‐bromo‐4‐iodo‐2,3,5,6‐tetrafluorobenzene, 2C7H10N2·C6BrF4I, and 1,2‐dibromo‐4,5‐difluoro‐3,6‐diiodobenzene, 2C7H10N2·C6Br2F2I2, are reported. In all five structures, the core halogen‐bonded 2:1 trimolecular units have geometrically similar parameters, with the central halogen‐bond donor flanked by two pyridine halogen‐bond acceptors twisted with respect to the central halogen‐bond donor at angles ranging from 76 to 86°. The I…N halogen‐bond separations are all short, ranging from 73.3 to 76.7% of the sum of the van der Waals radii, while the C—I…N bond angles are essentially linear. The Br…N halogen‐bond separation in the cocrystal formed with 1‐bromo‐4‐iodo‐2,3,5,6‐tetrafluorobenzene is 80.4% of the sum of the van der Waals radii. Subtle differences in the crystal packings are attributed to the role of secondary C—H…π and weak π‐type interactions with chloro and bromo substituents. The cocrystals 2C7H10N2·C6Cl4I2 and 2C7H10N2·C6Br4I2 are isomorphous. The role of secondary noncovalent interactions in the structures of a series of 2:1 cocrystals of ditopic halogen‐bond donors and 4‐(dimethylamino)pyridine is analyzed.