Pentti Pekonen

Homo- and heteroatomic chalcogen rings

Abstract 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 77 Se and 125 Te 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.

The Formation of Se10 and Se5S5. an Ab Initio Mo Feasibility Study

Ab initio MO calculations have established the structural and stability relationships of S10, Se10, and the three isomers of l,2,3,4,5-Se5S5. The calculations imply that ten-membered selenium-containing chalcogen rings should be sufficiently stable to render their preparation possible.

Small Chalcogen Rings

Abstract The reaction of [Ti(C5Me5)2S3] with Se2Cl2 produces 1,5-Se2S5, 1,2,3,4,5-Se5S3, and 1,2-Se2S6 as the main end products. This implies the existence of 1,2-Se2S3 as an initial reaction product the decomposition of which proceeds with parallel selenium atom transfer and dimerization reactions.

Selenium-77 nuclear magnetic resonance identification of seven-membered selenium sulfide ring molecules

Seven-membered heterocyclic selenium sulfides were prepared from a mixture of [Ti(C5H5)2SexS5–x] species (Se : S = 3 : 2)1 upon treatment with S2Cl2 and Se2Cl2, and the products identified with 77Se NMR spectroscopy. The assignment of the spectra was based on the known chemical shifts, and on the well established trends in the chemical shifts. The reaction of 1 with S2Cl2 produced 1,2,3,4,5-Se5S2, 1,2,3,4-Se4S3, 1,2,3-Se3S4 and 1,2-Se2S5, and that with Se2Cl2 produced Se7, 1,2,3,4,5,6-Se6S, 1,2,3,4,5-Se5S2, 1,2,3,5,6-Se5S2 and 1,2,4,5-Se4S3. A comparison of the predicted product distribution from the known composition of the starting [Ti(C5H5)2SexS5–x] mixture to that determined semiquantitatively from the peak intensities supports the spectral assignment.