Reaction of thiones with dihalogens; comparison of the solid state structures of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione-diiodine, -dibromine and -iodine monobromide

Reaction of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione 1 with diiodine or iodine monobromide in CH2Cl2 resulted in the formation of molecular charge-transfer complexes 1 . I-2 and 1 . IBr respectively. Both complexes have been characterised crystallographically and contain a linear S-I-X (X = I or Br) moiety with the sulfur adopting a tetrahedral geometry taking into account the stereochemically active lone pairs. The S-I [2.716(3)] and I-I [2.808(3) Angstrom] bond lengths in 1 . I-2 are similar to those reported for diiodine complexes of related thione donors. The adduct 1 . IBr is the first crystallographically characterised thione-iodine monobromide charge-transfer complex. The S-I distance [2.589(2) Angstrom] is shorter than that in 1 . I-2, consistent with IBr being a stronger acceptor than I-2. The I-Br distance [2.7138(11) Angstrom] is lengthened with respect to that in unco-ordinated IBr, but within bonding distance when compared to the sum of the van der Waals radii for iodine and bromine (3.75 Angstrom). Treatment of 1 with dibromine under identical conditions resulted in the formation of the adduct 1 . Br-2 and the dithiolylium salt [C5H6S4Br][Br-3]. 1/2Br(2) 2. Treatment of 1 with Br-2 in toluene led to the isolation of 1 . Br-2 only. The crystal structure of 1 . Br-2 shows the compound to contain a linear Br-S-Br moiety with the sulfur in a T-shaped or Psi-trigonal bipyramidal environment (taking into account the stereochemically active lone pairs). The structure of 2 reveals a three component system consisting of the [C5H6S4Br](+) cation, the [Br-3](-) anion and a molecule of Br-2 in a 2:2:1 ratio. These components are held in the lattice by a series of weak intermolecular interactions which link the tribromide ions and dibromine molecules into zigzag chains.