The Structures of S 4 N⊖, S 3 N 2 O 2 and S 4 N 3

Part of the potential surface of S 4 N⊖ has been investigated using the MNDO method. It is found that the cis-trans isomer 1b is more stable by 20-30 kJ/mol than the trans-trans isomer (1 c) and the cis-cis isomer (1 a). The stability of 1 b is traced back to stabilization of the HOMO and to a Coulomb attraction. For S 3 N 2 O 2 (2) the MNDO calculations favour those isomers (2a and 2b) with two sickle-like arrangements for the same reasons. For S 4 N 3 e (3) only one isomer (3a) is favoured due to the stabilization of the HOMO. The similarity in the transannular interaction present in 1-3 and that in trithiapentalenes and related compounds is pointed out. The PE spectrum of 2 has been reinvestigated. The first five bands can be interpreted by comparison between the measured ionization potentials and the calculated (MNDO) orbital energies.