Abstract
The well-known tendency of sulfur to catenate is exemplified by an extensive series of polysulfide dianions [Sn]2- (n = 2-9) and related radical monoanions [Sn]˙-. The dianions can be isolated as crystalline salts with appropriate cations and structurally and spectroscopically characterized. Although the smaller radical monoanions may be stabilized in zeolitic matrices, they are usually formed in solution via disproportionation or partial dissociation of the dianions as well as by electrochemical reduction of elemental sulfur. An understanding of the fundamental chemistry of these homoatomic species is key to unravelling their behaviour in a broad variety of chemical environments. This review will critically evaluate the techniques used to characterize polysulfide dianions and radical anions both in solution and in the solid state, i.e. Raman, UV-visible, EPR, NMR and X-ray absorption spectroscopy, X-ray crystallography, mass spectrometry, chromatography and high-level quantum-chemical calculations. This is followed by a discussion of recent advances in areas in which these anionic sulfur species play a crucial role, viz. alkali-metal-sulfur batteries, organic syntheses, biological chemistry, geochemical processes including metal transport, coordination complexes, atmospheric chemistry and materials science.
Highlights
The p-block element sulfur[1] is the tenth most abundant element in the universe
Longer-chain polysulfide ions with up to nine sulfur atoms were detected by negative ion mass spectrometry when the dianions were protonated to [HSn]À during electrospray using methanolic solutions with ammonium acetate buffer as reported by Gun et al in 2004.47 In that case the overall charge of the gaseous anions is reduced by 50%
In contrast to the behaviour of polysulfide dianions in electron-pair donor solvents, Yellowlees and co-workers found that the formation of the blue trisulfide radical anion [S3]À only occurs to a small extent in the ionic liquid [C4mim][DCA] (C4mim = 1-butyl-3-methylimidazolium; DCA = dicyanamide).[69]
Summary
The p-block element sulfur[1] is the tenth most abundant element in the universe. The crown-shaped structure of the most stable allotrope, cyclo-S8, is well-known as is the fact that elemental. Ralf Steudel is emeritus professor of inorganic chemistry at the Technical University Berlin, Germany He is best known for his many contributions to the chemistry of sulfur and selenium as well as for his textbooks and monographs on various aspects of inorganic chemistry. The broad significance of elemental sulfur and many inorganic sulfur compounds in the geo-, bio- and cosmo-spheres, has been recognized for more than thirty-five years.[14] Contemporary interest has been focused on the chemical properties of polysulfide dianions and the radical anions derived from them in part because of their function in alkali metal–sulfur batteries,[15] and owing to their role in a variety of other environments. We will attempt to provide a critical overview of the important developments that have appeared since previous reviews on these species.[6,7,8]
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