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 I2 and Br2. The detailed structural analyses of the cocrystals and salts reveal that the amide to amide N–H···O hydrogen bonding plays the major role in the cocrystals, while N–H···N hydrogen bonding predominates in the salts. With an increase in the halogen content in the lattice the interactions involved with halogens (N–H···X hydrogen bonding, N···X and X···X halogen bonding) are found to overpower the conventional N–H···O and N–H···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···N or N–H···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···Br–C, Br···Br, C–H···Br) in their crystal lattice.