HOMOATOMIC AND HETEROATOMIC CHALCOGEN RINGS

This review describes recent progress in the chemistry of homo- and heterocyclic chalcogen species summarizing their preparation, structural characterization, bonding, and spectroscopic properties. Although it is possible to prepare stoichiometrically pure chalcogen rings, many reactions result in the formation of complicated mixtures. The crystal and molecular structures of many homocyclic rings are known. All heterocyclic rings, however, are disordered and therefore it has not been possible to determine accurate bond parameters for them. The identification of individual molecular species and the composition of mixtures of chalcogen ring molecules have been studied successfully with HPLC and Raman spectroscopy, as well as with Se-77 and Te-125 NMR spectroscopy. With development of computing techniques, it has been possible to perform MO calculations with increasing sophistication. They have yielded reliable predictions on ground state geometries and electronic structures of different chalcogen rings. The emphasis of research in recent years has shifted from purely structural studies towards understanding the facile interconversion reactions that take place between the different chalcogen rings. The experimental and theoretical evidence on the mechanism of these ring interconversion pathways are discussed.