Structural and DFT studies of dibromine and diiodine adducts of a sulfur-rich thiocarbonyl donor

Mancini A.;Pala L.;ARAGONI, MARIA CARLA;ARCA, MASSIMILIANO;Devillanova F. A.;Hursthouse M. B.;Light M. E.;Skabara P. J.;Bricklebank N.

2012-01-01

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Abstract

4,5-Bis(benzoylthio)-1,3-dithiole-2-thione (1) forms molecu- lar adducts with dibromine (2) and diiodine (3), which display a range of complementary primary X–X and S–X and second- ary 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 asym- metry 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 fea- turing 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 interme- diate [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 accom- modate I2 molecules as “guests”, in one case the guest di- iodine molecule bonds with the sulfur atoms of the benzo- ylthio-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 inter- acts with two additional I2 molecules leading to infinite chains in the [01–1] direction.