Investigations on organo-sulfur-nitrogen rings and the thiocyanogen polymer, (SCN)x

Article abstract of DOI:10.1002/chem.200501528

The synthesis and full characterisation of a series of 1,2,4-thiadiazoles is reported. (SCN)_x has been studied by a variety of techniques and the data compared with 1,2,4-thiadiazole and 1,2,4-dithiazoles. The observed data suggest that the polymer consists of 1,2,4-dithiazole rings linked by nitrogen atoms. For (SCN)_x, the MALDI-TOF mass spectroscopy showed a parent ion at 1149 and a series of peaks with (SCN)₂ repeat units (116 m/z); this result implies that (SCN)₂ may be the monomer unit of the polymer. Its IR spectrum shows a very broad peak with maximum at 1134 cm^-1 consisting of several overlapping peaks in the same region as ring vibrations for 1,2,4-thiadiazole and 1,2,4-dithiazole compounds. Peaks in the Raman spectrum in the range 400-480 cm^-1 support the presence of disulfide units within the polymer. The solid-state ¹³C NMR (99% ¹³C-labelled) spectrum is dominated by two singlets of equal intensity at approximately 187 and 184 ppm with low intensity peaks in the range 152-172 ppm, in approximately the same range as both 1,2,4-thiadiazoles and 1,2,4-dithiazoles. The solid-state ¹⁵N NMR (99% ¹⁵N labelled) spectrum displays two major peaks of similar intensity at 236.9 and 197.2 ppm, which are clearly very different environments to those observed in bis(3-bromo-1,2,4-thiadiazol-5-yl) disulfide, but similar to 1,2,4-dithiazoles. The X-ray structures of seven C-S-N systems are reported. Preliminary studies on (SeCN)_x suggest that literature references to this polymer may be in error with the red solid actually being red selenium.