Preparation and crystal structures of two phosphorus–sulphur rings: (PhP)₃S₃and (PhP)₂S₄

The 1 : 1 reaction between PPhCl2 and (SnMe3)2S in CS2 provides a convenient direct route to (PhP)3S3(1), which reacts with elemental sulphur to give (PhP)2S4(2). Both structures have been determined by X-ray diffraction using twinned crystals. Compound (1) is monoclinic, space group P21, with a= 8.884(2), b= 13.713(2), c= 8.309(2)Å, β= 106.61 (2)°, Z= 2, and R= 0.051 for 1 938 unique observed reflections. The structure contains an unsymmetrical five-membered ring with one exocyclic sulphur, and does not agree with a previous proposal based on n.m.r. data. Compound (2) is monoclinic, space group P21/c, with a= 6.624(1), b= 14.438(3), c= 7.667(2)Å, β= 95.31(2)°, Z= 2, and R= 0.060 for 880 unique observed reflections. The four-membered ring with two trans exocyclic sulphurs possesses a crystallographic centre of symmetry.