Halogen Bonding in Halothiophene Building Blocks

Abstract

<p>Thiophenes bearing monotopic and symmetric ditopic halogen substituents and asymmetric ditopic halogen and pyridine substituents that act as halogen bond acceptors were evaluated for their halogen bonding interactions with 1,4-diiodotetrafluorobenzene and N-iodosuccinimide. The combinations resulted in C/N-I···X′ (X′ = Cl, Br, I) and C/N-I···N_Py (Py = pyridine) interactions, the former characterized by an interaction energy (ΔE_int) ranging from −4.4 to −18.7 kJ mol^-1 and the latter from −26.3 to −56.0 kJ mol^-1. X-ray crystallography studies show that the ditopic asymmetric systems consisting of both halogens and pyridine self-associate through C-X···N_Py (X = Cl, Br, I) halogen bonding, and in their optimized structures the energies range from −5.4 to −19.6 kJ mol^-1 depending on the type of halogen atom present. The ¹H NMR association constants of N-I···N_Py halogen bonds range between 1405 and 6397 M^-1. The σ-hole strengths of halogens have been useful in describing the interaction energies and solution models.</p>