Interplay of Halogen Bonding and Hydrogen Bonding in the Cocrystals and Salts of Dihalogens and Trihalides with N,N′-Bis(3-pyridylacrylamido) Derivatives: Phosphorescent Organic Salts

N,N'-Bis(3-pyridylacrylamido) derivatives are shown to form cocrystals and salts with the dihalogens I-2 and Br-2. The detailed structural analyses of the cocrystals and salts reveal that the amide to amide N-H center dot center dot center dot O hydrogen bonding plays the major role in the cocrystals, while N-H center dot center dot center dot N hydrogen bonding predominates in the salts. With an increase in the halogen content in the lattice the interactions involved with halogens (N-H center dot center dot center dot X hydrogen bonding, N center dot center dot center dot X and X center dot center dot center dot X halogen bonding) are found to overpower the conventional N-H center dot center dot center dot O and N-H center dot center dot center dot N hydrogen bonding. In one such heavy halogen content salt, it is found that the water acts as a mere space-filling species and is not involved in any conventional hydrogen bonding such as N-H center dot center dot center dot N or N-H center dot center dot center dot O hydrogen bonds or halogen bonding. All of the cocrystals and salts are found to exhibit solid-state photoluminescence, which can be attributed to the charge transfer due to halogen bonding. Further, the tetrabrominated salts are found to exhibit phosphorescence at 77 K in a rigid matrix and also at room temperature owing to triplet-producing carbonyls and triplet-stabilizing heavy-atom perturbations (C-Br center dot center dot center dot Br-C, Br center dot center dot center dot Br, C-H center dot center dot center dot Br) in their crystal lattice.