Selenium-77 NMR spectroscopic study of fluxional selenium sulfide 1,2,3,4,5-Se5S2

The {sup 77}Se NMR spectrum has been recorded for the fluxional heterocyclic selenium sulfide 1,2,3,4,5-Se{sub 2}S{sub 5}, which has been prepared from the {sup 77}Se-enriched (Ti(C{sub 5}H{sub 5}){sub 2}Se{sub 5}) (enrichment 94%) and from S{sub 2}Cl{sub 2}. The spectrum shows three second-order multiplets at 1087.1, 1025.0, and 978.9 ppm (relative to Me{sub 2}Se) corresponding to a five-spin (AMM{prime}XX{prime}) system. A simulation enables the complete assignment of all transitions to be made and yields the refined values of all {sup 77}Se-{sup 77}Se coupling constants. The number of NMR signals, their coupling pattern, and the values of the spin-spin coupling constants are consistent with the concept of facile pseudorotation in the seven-membered chalcogen-containing ring molecules. 20 refs., 4 figs., 1 tab.