Crystal, molecular, and ?-electronic structure of 1,3,2-benzodithiazolium chloride

X-Ray diffraction examination and MNDO calculations have shown that 1,3,2-benzodithiazolium chloride (I) is ionic, with a planar heteroaromatic 10π-electron cation. The π-MO of the cation (I) is isolobal with the p-MO of benzo-2,1,3-thiadiazole. In the cation of (I), as in the latter compound, the p-AO of nitrogen and sulfur contribute for the most part to π-MO of differing symmetry (b1 and a2, respectively). This has the consequence that although both nitrogen and sulfur participate in the formation of a single π-system in the thiazolium cation of (I), there is virtually no π-bonding between them. Generally speaking, the π-MO of the (I) cation shows a tendency to localization on separate molecular fragments. The charge on the cation is localized at the SNS group, and the five-membered ring is strongly polarized. These features all reduce the heteroaromaticity of the system.