Polychalcogenides

Ruhr-Universitat Bochum, Fakultat fur Chemie, Lehrstuhl fur Analytische Chemie, D-44780, Bochum, Germany 

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Polychalcogenides are less stable than polysulfides (p. 681). Reaction of alkali metals with Se in liquid ammonia affords M2Se2, M2Se3 and M2Se4, and analogous polytellurides have also been reported (see preceding section). However many of these compounds are rather unstable thermally and tend to be oxidized in air. 

The preparation of some polychalcogenide solids can be achieved at 200-450 °C by molten salt (flux) methods. The reaction of tin with alkali metal sulfides in the presence of Ss at 200-450 °C gives a variety of alkali metal tin sulfides depending on the ratio of the starting materials, the reaction temperature, and the alkah metals (Scheme 30) [90]. These alkali metal tin sul-... 

Evain M, Brec R (1992) A New Approach to Structural Description of Complex Polyhedra Containing Polychalcogenide Anions. 79 277-306... 

The characteristic strong tendency of sulfur and its heavier congeners to catenate is reflected in the wide range of polychalcogenide ions, i.e., reduced forms of the elements, that may be discrete in highly ionic salts or dissolved in polar solvents. 

Sheldrick WS (2007) Polychalcogenides. In DevrUanova FA (ed.), Handbook of chalcogen chemistry New perspectives in sulfur, selenium and tellurium, Royal society of Chemistry Cambridge, UK... 

Kanatzidis MG, Huang SP (1994) Coordination chemistry of heavy polychalcogenide ligands. Coord Chem Rev 130 509-621... 

In screening electrolyte redox systems for use in PEC the primary factor is redox kinetics, provided the thermodynamics is not prohibitive, while consideration of properties such as toxicity and optical transparency is important. Facile redox kinetics provided by fast one-electron outer-sphere redox systems might be well suited to regenerative applications and this is indeed the case for well-behaved couples that have yielded satisfactory results for a variety of semiconductors, especially with organic solvents (e.g., [21]). On the other hand, many efficient systems reported in the literature entail a more complicated behaviour, e.g., the above-mentioned polychalcogenide and polyiodide redox couples actually represent sluggish redox systems involving specific interactions with the semiconductor... 

Elhs AB, Kaiser SW, Bolts JM, Wrighton MS (1977) Study of n-type semiconducting cadmium chalcogenide-based photoelectrochemical cells employing polychalcogenide electrolytes. J Am Chem Soc 99 2839-2848... 

The field of polysulfide complexes has been reviewed earlier.347 A more recent survey covers polychalcogenide complexes in general,348 and in a review on ate complexes also further examples of anionic polychalcogenide species are dealt with.349... 

Heavy ketones have been synthesized by several synthetic methods shown in Scheme 19 (i) the reaction of divalent group 14 element species with chalcogen sources, (ii) the reaction of dihydrometallanes with chalcogen sources, (iii) the dechalcogenation of metal polychalcogenides, (iv) the reaction of dilithiomet-allanes with dihalochalcogenides, and (v) substitution of the chloro group of heavy acyl chlorides. The methods used for the synthesis of heavy ketones are summarized in Tables 3-5. 

Three general methods are available for the preparation of polychalcogenides ... 

Aqueous or methanolic solutions of alkali metal carbonates induce disproportionation of chalcogens to oxoanions and polychalcogenides E under solvothermal conditions.11 Potential redox equilibria such as (1) are driven to the right at 120-200°C by the development of C02. 

Polychalcogenides form chain fragments E2- that are in dynamic equilibrium with one another both in solution and in molten alkali metal fluxes. Longer chains (n = 3-6) can exist in significant concentrations at the relatively low temperatures employed for mild solvothermal syntheses (120-200°C), but are unstable with respect to disproportionation reactions of type (2) at higher temperatures. 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

Radical anions are also present in solutions of sulfur in oleum and in various polychalcogenide fluxes. However, only one radical ion Sg has been successfully characterized in the solid state, namely in [Ph4P]S6, which can be prepared according to Equation (3) by treating Ph4P]N3 with H2S in the presence of trimethylsilyl azide.35... 

Metal sulfides and polysulfides have been extensively studied because of their key role in important catalytic processes such as the hydrodesulfurization of crude oil or the biosynthesis of metalloproteins. The coordination chemistry of polysulfides85 86 has been comprehensively reviewed similar to that of the heavier polychalcogenides.10,12 15 Polysullido complexes are themselves reactive and their exothermic desulfurization can be exploited as a means of... 

Alternatively, the polychalcogenide may be generated in situ and then allowed to react immediately with the appropriate metal compound.89... 

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