Anion–π interactions in [S4N3]+ rings

Abstract

In 1996 J. Derek Woollins reported “π-facial” interactions between the chloride anion and the seven-membered aromatic [S₄N₃]⁺ and inorganic ring (Polyhedron, 1996, 15, 4603–4605). In spite of this manuscript has not been highlighted before (only 5 citations so far), it can be considered as a pioneering work in the field of noncovalent interactions involving anions, since unprecedented anion–π contacts were described as “π-facial” interactions. In this manuscript several complexes of [S₄N₃]⁺ with anions were optimized at the BP86-D3/def2-TZVPD level of theory and compared to X-ray structures retrieved from the CSD. We have evaluated the interaction energies between the chloride and nitrate anions and the [S₄N₃]⁺ ring. The anion–π complexes are energetically favourable and the complexation has been characterized by means of Bader's theory of “atoms in molecules”. Moreover, the π-orbitals of the [S₄N₃]⁺ ring have been computed and the aromaticity of the 10-π electron seven membered ring was analysed.