APPLICATION OF DICYANOHEXASULFANE FOR THE SYNTHESIS OF CYCLO-NONASULFUR - CRYSTAL AND MOLECULAR-STRUCTURES OF S-6(CN)(2) AND OF ALPHA-S-9

A novel synthesis for dichlorotetrasulfane is reported. Careful chlori nation of cyclo-hexasulfur yields S4Cl2 (besides S2Cl2), which is used to prepare S-6(CN)(2) by reaction with Hg(SCN)(2). An X-ray diffracti on analysis of S-6(CN)(2) shows nonhelical chainlike molecules with th e following molecular parameters: SS bond lengths 203.4-207.4 pm, SSS valence angles 104.95-105.96 degrees, SS torsion angles 81.2-94.5 degr ees (motif: ++--+). The chain-terminating SCN groups exhibit a paralle l orientation within the molecules and are antiparallel in neighboring molecules. S-6(CN)(2) reacts with titanocene pentasulfide to give S-9 and titanocene diisothiocyanate, alpha-S-9 was obtained as single cry stals, the structure of which was determined by X-ray diffraction. The two independent molecules occupy sites of C-1 symmetry, but the molec ular symmetry is approximately C-2, in agreement with predictions by d ensity functional and nb-initio MO calculations. Molecular parameters: bond lengths 203.2-206.9 pm, valence angles 103.7-109.7 degrees, tors ion angles 59.7-115.6 degrees (motif: ++--++-+-). The average SS bond lengths in S-6(CN)(2) and alpha-S-9 agree with the single-bond value o f 205 pm as observed in H2S2 and in alpha-S-8.