The quest of radical cations of the heavier chalcogenides

Abstract

In the course of this work various new compounds were synthetized and characterized by common methods. The well-defined dibenzodioxine type heterocycle phenoxatellurine (PT) was investigated in its behaviour towards single electron oxidating reagents, such as nitrosonium salts, resulting in diamagnetic double decker respectively triple decker structures which can be described as dimers of the elusive radical cation [PT]•+.

The stacking derives not just from London dispersion interactions and non-covalent multi-centre bonding between the tellurium atoms, but also from SOMO-SOMO interactions between two radical cations [PT]•+, also known as “pancake” bonding, which can be realized due to the change in the conformation of the PT units upon oxidation. The oxidations with nitrosonium hexafluoroantimonate gave rise to a phenoxatellurine double decker cation, whereas the tetrafluoroborate salt gave rise to a triple decker structure.

The reaction of PT with triflic acid led to relatively air stable triple decker structures in three different modifications, which were investigated by Hirshfeld surface analysis. Upon exposure to moist air for several weeks an oxo-bridged dimer or trimer structure evolved.

Based on the well known behaviour as a donor the first PT charge-transfer complex with 1,2,5-thiadiazole derivatives was prepared and characterized. Upon gasphase cocrystalization a complex in ratio of 1:3 in favour of the thiadiazole acceptor was obtained. Furthermore an octahedral complex by the reaction of (CO)5MnBr with PT was obtained, that has two PT ligands situated in cis-position, similar to the structure described by Hieber and Kruck in 1962.

In 1926 Drew discovered intensively colored solutions by dissolving PT in conc. sulphuric acid. Almost 100 years later the nature of one of those species, which is responsible for the color, has been unravelled. X-ray diffraction reveal a PT double decker structure with hydrogensulphate ions associated via secondary interactions.

The condensation reaction of 4,4’-dimethyldiphenylether with tellurium tetrachloride afforded 2,8-dimethyl-10,10-dichlorophenoxatellurine which shows, compared to the unsubstituted PT, a planar structure in which the Cl atoms are arranged in the axial positions, while the two C atoms are arranged in the equatorial positions. Attempts on reducing the structure to 2,8-di-methylphenoxatellurine were unsuccessful.

Isoelectronic to the neutral PT, dibenzo[b,e][1,4]iodaoxin-5-ium 4-methylbenzenesulphonate [C12H8OI][O3S(p-C6H4Me)] was prepared. The phenoxaiodonium ion possesses also a butterfly-like conformation with nearly identical I-C bond length compared to Te-C in phenoxatellurine.

The first 8-methoxanaphthyltellurium compounds have been introduced enhancing the variety of peri-substitutes naphthyl and acenaphthyl species. Furthermore new acenaphthene compounds have been obtained with a diphenyphosphino-group in the 5-position and phenylchalcogenes in 6, opening a new path for oxidization to chalcogen radical cations.

Moreover organotellurium compounds with bulky 2,6-dimesitylphenyl groups, namely 2,6-dimesitylsulphide, 2,6-dimesitylphenylselenide and 2,6-dimesitylphenyltelluride were synthetized and characterized. First attempts of oxidizing 2,6-dimesitylphenyltelluride with nitrosonium hexafluoroantimonate led to the 2,6-dimesitylphenylhydroxyltelluronium hexafluoroantimonate.