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

Abstract

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·I₂ 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) Å] bond lengths in 1·I₂ 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) Å] is shorter than that in 1·I₂, consistent with IBr being a stronger acceptor than I₂. The I–Br distance [2.7138(11) Å] 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 Å). Treatment of 1 with dibromine under identical conditions resulted in the formation of the adduct 1·Br₂ and the dithiolylium salt [C₅H₆S₄Br][Br₃]·½Br₂ 2. Treatment of 1 with Br₂ in toluene led to the isolation of 1·Br₂ only. The crystal structure of 1·Br₂ shows the compound to contain a linear Br–S–Br moiety with the sulfur in a T-shaped or Ψ-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 [Br₃]^– anion and a molecule of Br₂ 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.