4-Phenyl-l,2-dithia-3,5-diazolium chloride on reduction with thiocyanate ion gives the black air-sensitive title compound, (PhCN2S2)2. Crystals have been studied by means of X-ray diffraction at room temperature. The compound crystallizes in the space group P2,2,2, (no. 19) with a = 16.061 (1 ), b = 32.984(5), and c = 5.774 O(4) A, and Z = 8. The crystal structure has been solved using 2 51 3 reflections and refined to a final R value of 0.082. Each asymmetric unit contains two (PhCN2S2)2 molecules. Within each dimer the bridging mean S S distance is 31 0.9(5) pm. The two half-molecules within each dimer are nearly parallel and are slightly twisted with respect to each other. The short (mean) CNBS2 ring distances (dcN = 133, dRN = 162, and d,, = 209 pm) and the PhCN2S2 coplanarity suggest that the rings are aromatic with one electron pair delocalized at the four (disulphide) sulphur atoms.1-CHLORO-1,2,4-TRITHIADIAZOLIUM, CHLORIDE, which Contains the six x-electron cation S3N2C1+, can be converted, by heating in vacuo,l to the compound S,N,Cl. Crystal structure determinations of the analogous S3N,(AsF,) and S3N2(S@,)C1 revealed the presence of S,N2 rings associated in pairs. Each pair appeared to be held together by a four-centre interaction involving the adjacent sulphur atoms of the two rings.3Since S,N,Cl+ and PhCN,S,+ are isoelectronic, we have studied reductions of the latter and have carried out a structural study of the product which, like S3N,+, is associated in the lattice in pairs with further weaker interactions between the pairs. In each (PhCN,S,)2 unit, the five-membered rings adopt an almost eclipsed cis conformation in contrast to the stepped trans conformation of (S,N,),2+. EXPERIMENTAL ' J.
