Isolation of the First Six‐ and Seven‐Membered Selenium‐Sulfur Rings and Mechanism of their Conversion into Other‐Sized Rings

Se2S5, the first cyclic selenium sulfide of type SexSy with x + y = 7, was prepared from titanocene pentasulfide and dichlorodiselane. In solution, Se2S5 forms Se3S5 and SeS5 (the first SexSy species with x + y = 6). A spirocyclic intermediate 1 is proposed for the decomposition reaction.