CNDO/2 localized molecular orbital studies for the isoelectric cations cyclo- 1,3,4-trithiadiazole(2+) and cyclo-2,5-dithiatrizole(1+)

Abstract

The electronic structures of cyclo-1,3,4-trithiadiazole(2+) and cyclo-2,5-dithiatrizole(1+) ions have been studied using energy localized CNDO/2 molecular orbitals. cyclo-1,3,4-trithiadiazole(2+) was found to have five σ-bonds forming the sigma skeleton of the ring, one lone pair orbital on each atom and six π-electrons. No π-bonding was observed between the two adjacent sulfur atoms. cyclo-2,5-dithiatrizole(1+) possesses a sigma bond structure and one lone pair orbital on each atom. It has six π-electrons, two between the adjacent nitrogen atoms and the remaining four delocalized over the SNS segment of the molecule. The enhanced stability of the S 3N 2+ 2 cation relative to the isoelectronic S 2N + 3 can be attributed to the larger tendency of an apical sulfur atom to participate in three center to two electron π bonding relative to the lack of ability of an apical nitrogen to do the same.