NMR SPECTROSCOPIC EVIDENCE FOR THE EXISTENCE OF TELLURIUM-CONTAINING CHALCOGEN RINGS AND POLYMERS IN SULFUR TELLURIUM AND SULFUR SELENIUM TELLURIUM MELTS

The composition of sulfur-rich molten mixtures of sulfur. selenium, and tellurium has been studied by using Te-125 and Se-77 NMR spectroscopy at 145-degrees-C. The spectral assignments and the identification of the molecular species were made on the basis of combined information from the natural abundance and from the Se-77- and Te-125-enriched samples (enrichment in both cases 92%), taking the known trends in the Se-77 and Te-125 chemical shifts into account. The melts were found to contain cyclic chalcogen molecules in equilibrium with polymeric chains. The main tellurium-containing chalcogen ring in the binary sulfur-tellurium melts was TeS7 [delta(Te) = 1316 ppm]. The presence of small amounts of 1,2-Te2S6 [delta(Te) = 1126 ppm] and its other isomers could also be inferred. The ternary sulfur-selenium-tellurium mixtures contained binary heterocycles SeS7, all isomers of Se2S6, TeS7, and 1,2-Te2S6 as well as its other isomers. The presence of 1,2-TeSeS6 [delta(Te) = 1148 ppm; delta(Se) = 493 ppm, 1J(TeSe) = 50 Hz] and 1,3-TeSeS6 [delta(Te) = 1364 ppm, 2J(TeSe) = 220 Hz] was indicated by the Se-77 and Te-125 NMR spectroscopic data of the enriched sample. The presence of 1,4- and 1,5-isomers of TeSeS6 Could also be inferred from the Te-125 spectrum of the enriched samples. The NMR signals of the sulfur-tellurium and sulfur-selenium-tellurium polymeric material can be interpreted in terms of the statistical distribution of -S-Te-S-, -Te-Te-S-, and -Te-Te-Te- fragments. The ternary melts also show the resonances clue to -Se-Te-S- in the Te-125 spectrum and those due to -Te-Se-S-in the Se-77 spectrum. All samples studied in this work also contain both homocyclic and polymeric sulfur species.