The structures and stabilities of singlet and triplet dithiatriazines: a computational study

Ab initio molecular orbital and Møller-Plesset perturbation theory calculations have been carried out on two model dithiatriazines RCN 3 S 2 (R = H, NH 2 ). With geometry optimization and the inclusion of electron correlation both of these dithiatriazines are predicted to be ground state singlets. Both molecules have low-lying triplet excited states, with energy gaps of 6.6 (R = H) and 13.0 (R = NH 2 ) kcal mol −1 . The singlet dithiatriazines distort from high (C 2v ) to low (C s ) symmetry, and these changes are important in determining the relative energies of the singlet and triplet molecules. The structural distortions experienced by these molecules are related to Hartree-Fock and Jahn-Teller instabilities in other thiazene heterocycles.