Novel Supramolecular Heterosynthons [C-I···N═N] and [C-I···π(C≡C)]

Heteromolecular C-I···π(C≡C) and C-I···(LEP)N═N (LEP lone electron pair) have been observed for the first time in cocrystals of diphenylacetylene (tolan, Ph₂C₂) and azobenzene (Ph₂N₂) with halogen bond donor, diiodoacetylene (C₂I₂). Computational analysis (density functional theory (DFT), molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM)) indicates that C-I···π(C≡C) and C-I···(LEP)N═N interactions are stronger than I···π(Ph), which is also possible between iodo-XB donors and Ph₂C₂ or Ph₂N₂. However, cocrystallization of Ph₂C₂ and Ph₂N₂ with isomeric series of o-, m-, p-diiodotetrafluorobenzenes (1,2-, 1,3-, 1,4-DITFB) and pentafluoroiodobenzene (C₆F₅I) afforded the cocrystals stabilized predominantly by the relatively weaker I···π(Ph) interactions, while 1,3-DITFB featured both I···π(C≡C) and I···π(Ph) halogen bonds. Analysis of the interplay of intermolecular interactions and energetic, molecular symmetry, and packing factors in cocrystals revealed a complex structural landscape and suggested the lowering of molecular symmetry to achieve the desired [C-I···π(C≡C)] and [C-I···(LEP)N═N] for diiodotetrafluorobenzene coformers. Besides these promising structural motifs, we discuss here the formation of chiral cocrystal structures from achiral coformers and high-Z′ structure Ph₂N₂ 1,2-DITFB (2:3).