HETEROCYCLIC CATIONS WITH DELOCALIZED PI-SYSTEMS AND SHORT INTRAMOLECULAR SULFUR ... SULFUR CONTACTS - THE STRUCTURES OF 2 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 fu nction of the orientation of the groups, with the shortest contacts oc curring when the groups are coplanar. A lower limit for the latter is indicated by the structures of the -benzodithiol-2-ylidenemethyl)-1,3- 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 intramol ecular sulfur...sulfur contact distances, 0.5-0.7 Angstrom within the sum of traditional van der Waals radii, and maximised by in-plane angu lar distortions, indicate a lower limit to the effective size of the b onded divalent sulfur atom of ca. 1.45 Angstrom.