Nature of S ⋯· O interaction in short X –S ⋯· O contacts: charge density experimental studies and theoretical interpretation

Abstract

2-(2-Chlorobenzoylimino)-1,3-thiazolidine (I) and 3-benzoylimino-4-methyl-1,2,4-oxathiazane (II) present short intramolecular S ⋯· O contacts of 2.68 and 2.24 Å, respectively. X-Ray and neutron diffraction at 122 K performed on (II), for comparison with (I), already studied, led to experimental charge density deformation maps which exhibit a strong peak around the sulphur atom. Using simple molecular orbital theory, it is possible to interpret the shortening of S ⋯· O distances in these compounds by σ-type interaction between the oxygen p and the sulphur p and d orbitals. The significant variation of the equilibrium S ⋯· O distance with the nature of the atom bonded to S is explained in terms of the strength of the coupling between X–S antibonding orbital and oxygen ione-pair orbitals.