Hartree–Fock instabilities in the trisulphur–trinitride anion

Abstract

Crystallographic evidence indicates that the structure of the trisulfur trinitride anion, S3N3−, is planar with equal SN bond lengths. Although the recent literature contains a number of molecular orbital calculations of D3h symmetry there are also calculations which indicate inequivalent nitrogens, suggesting broken symmetry. The results of an investigation of Hartree–Fock instabilities of the abinitio molecular orbital description of this system are reported. The D3h solution is indeed singlet stable but there are relatively close-lying C2v broken-symmetry solutions. In the broken-symmetry solutions the π electron network encompasses only five centres; the sixth centre, essentially free of π charge, may be either a sulphur or a nitrogen, thus yielding two distinct broken-symmetry solutions.