Halogen-Bonded Thiophene Derivatives Prepared by Solution and/or Mechanochemical Synthesis. Evidence of N•••S Chalcogen Bonds in Homo- and Cocrystals

Thiophene, a key building block for the construction of conjugated materials, has been scarcely studied in halogen bonding (XB)driven self-assemblies. In the present study, two thiophene derivatives modified at position 3 were (co-)crystallized using complementary XB donor/acceptor functional groups. Single-crystal X-ray diffraction analysis confirmed the presence of halogen and chalcogen bonding acting, in most cases, concomitantly. While the majority of the structures are governed by the conventional N center dot center dot center dot I motif, additional S center dot center dot center dot N and S center dot center dot center dot S contacts encouraged the cohesion of the supramolecular architectures. Density functional theory calculations shed the light on interaction energy, their respective contributions of the motifs to these non-covalent bonds, and the overall stability of these assemblies. To gain further insight into the formation and evidence of XB interactions, solution and mechanochemical syntheses of polymorphic adducts were performed, followed by 13C solid-state NMR analysis. Further, 1H and 19F{1H} solution-state NMR spectroscopy studies were carried out to highlight these interactions in the solution phase. The strength and directionality of halogen bonding thus reaffirm its role as a structure-directing agent for designing functional materials. The evidence of N center dot center dot center dot S chalcogen bonds in thiophene derivatives also broadens up the horizon of supramolecular chemistry in S-heterocycles, while necessitating further investigation for rational application in materials science.