Developments in Chalcogen-Halide Chemistry

This chapter presents an account of the current preparative and structural aspects of chalcogen-halide chemistry. The chapter focuses on the inorganic chemistry of the binary chlorides, bromides, and iodides as well as on the corresponding hypervalent anionic and cationic halo derivatives; fluorides are referred to in only a few cases. The chapter discusses the variability of the structural and bonding properties of the “inert pair” systems of the chalcogens in their formally lower positive oxidation states that directly influences the reactivity and the nature of the variety of possible reaction products. This field of chemistry may serve as a model for bonding, structure, and the reactive properties of analogous s2 systems of the neighboring elements, such as Sb(III), Bi(III), or I(V). Current investigations, for example, on antimony(III) and arsenic(III) halogen compounds, have indicated quite similar structural principles as in Te(IV) analogues. In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride and of tellurium tetrachloride on twinned crystals were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties, as well as the synthetic potential of the compounds. The chapter discusses the characteristic structural and bonding features of the halogen compounds of the chalcogen(IV) systems, in which the role of the inert pair determines much of the stereochemistry and reactive properties of the whole class of compounds. SCl4, as the only stable tetrahalide of sulfur besides SF4, is known to be easily prepared at temperatures below –34°C from the elements or from the reversible reaction of equimolar amounts of SC12 and chlorine.