2,5-Diiodothiophene: A Versatile Halogen Bonding Synthon for Crystal Engineering

Relative to the common diiodobenzene-based halogen bond donors, little is known about the halogen bonding of iodine-substituted thiophene compounds. A series of co-crystallization experiments were performed using the sulfur-atom-containing halogen bond donor 2,5-diiodothiophene with N-heterocyclic diamines, as well as ammonium iodide salts. These results reveal a wide range of halogen bonding motifs tied to the halogen bond donor/acceptor stoichiometry. While, in acceptor-rich stoichiometries, discrete units prevail through C–I···I halogen bonds, donor-rich stoichiometries encourage the formation of two-dimensional halogen bonding networks, often with the additional involvement C–I···S and S···S interactions. Halogen bonding through the C–I iodine atom predominates in all structures. The measured halogen bond distances fall between those typically observed for 1,4-diiodobenzene and 1,4-diiodotetrafluorobenzene, reaffirming the role of fluorination in strengthening the halogen bond while also expanding the library of halogen bonding synthons to donors having intermediate electrostatic potentials.