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Structural and DFT Studies of Dibromine and Diiodine Adducts of a Sulfur-Rich Thiocarbonyl Donor


  • Dedicated to the memory of the late Stephen M. Godfrey (1966–2011)


4,5-Bis(benzoylthio)-1,3-dithiole-2-thione (1) forms molecular adducts with dibromine (2) and diiodine (3), which display a range of complementary primary X–X and S–X and secondary S···X and X···X bonding interactions. Compounds 2 and 3 were characterised by X-ray diffraction analysis and FT-Raman spectroscopy. Compound 2, which is derived from the additive dibromine oxidation of 1, features a near linear Br–S–Br moiety that is coplanar with the dithiole-2-thione heterocycle. The S–Br bonds in 2 are asymmetric; the asymmetry arises mainly through a combination of intramolecular S···Br bonds between the Br atoms and the thioether S atoms of the donor, and an intermolecular S···Br contact between one of the bromine atoms and the hypervalent S atom of an adjacent molecule. DFT calculations carried out on 2 with different functionals agree and show that the geometry featuring the SBr2 moiety coplanar with the heterocycle is more stable by about 9 kcal mol–1 than that with the SBr2 unit perpendicular to the plane of the heterocycle. DFT calculations indicate that the formation of 2 can be explained based on the charge distribution on the hypothetical cationic intermediate [1–Br]+. Diiodine complex 3 is a molecular charge-transfer species, with an almost linear S–I–I moiety. The unit cell contains two molecules of donor 1, related by a centre of inversion, which form a dimer pair held together by two intermolecular S···S and two S···O contacts. The packing of the dimers generates various cavities that are able to accommodate I2 molecules as “guests”, in one case the guest diiodine molecule bonds with the sulfur atoms of the benzoylthio-groups and acts as a bridge between adjacent dimers, in another the diiodine is disordered along the channel-like cavity. The terminal iodine atom of each S–I–I fragment interacts with two additional I2 molecules leading to infinite chains in the [01–1] direction.