Heterocyclic cations with delocalised PI-systems and short intramolecular sulfur...sulfur contacts: The structures of two derivatives of the 2-(1,3-dithiol-2-ylidenemethyl)-1,3-dithiolium cation

The effective size of bonded divalent sulfur in S...S contacts is a function of the orientation of the groups, with the shortest contacts occurring when the groups are coplanar. A lower limit for the latter is indicated by the structures of the 2-(1,3-benzodithiol-2-ylidenemethyl)-l,3-benzodithiolium and 2-(1,3-dithiolan-2-ylidenemethyl)-1,3-dithiolanium cations, 2 and 3. These show almost mm symmetry with all four sulfur atoms involved in stabilisation of the positive charge. Short intramolecular sulfur...sulfur contact distances, 0.5-0.7 Å within the sum of traditional van der Waals radii, and maximised by in-plane angular distortions, indicate a lower limit to the effective size of the bonded divalent sulfur atom of ca. 1.45 Å.