Polysulphide Ions

The spectral maxima at 320, 390, and 590 nm were found to correspond to absorptions by the ions S , S , and S7, respectively. Direct observations (resonance Raman, i.r., and e.s.r. spectra) and indirect measurements (visible— u.v. spectra, conductivity, and magnetic susceptibility) strongly suggest that the intensely blue species formed by alkali-metal polysulphides or elemental sulphur in hexamethylphosphoramide can be attributed to the Sj radical anion. Cryoscopic, conductance, and magnetic measurements euid i.r. and u.v. spectral data have been used to study the cations formed in solutions of sulphur in disulphuric acid. The blue coloration was shown to be due to the formation of the Si ion and the colourless solutions were found to contain the S ion. The solid compounds S4S30ioand 8383010, formed by the action of SO3 on elemental sulphur in 8O2 media at low temperatures, have been isolated and characterized. 

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However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

Sulphur dissolves in solutions of soluble sulphides and forms a mixture of polysulphide ions, with chain lengths, 2—5. 

The atoms of a polysulphide ion are joined in chains coupled by single co-valent bonds. 

Since the stereochemistry of a molecule S 2R2 is similar to that of a sulphur chain S the following remarks apply equally to three main groups of compounds molecules S 2R2, polysulphide ions S , polythionate ions S Og and closely related molecules such as TeS i04R2. 

The dihedral angles of around 110° in the pentathionate and the related Se and Te ions may be compared with the much smaller values in polysulphide ions (p. 594). There appears to be a difference in length between the central and terminal S—S bonds comparable with that in the S ion. 

As shown by the eqns. (20-24) owing to the activity of the sulphide or polysulphide ion, the O—linkage is broken to form alkoxide and thionitrate or polythio-nitrate ions. In the other reactions the influence exerted by sulphide on the oxygen atom, which results in the creation of nitrite ions, has been taken into account. Both schemes indicate that the nitrite ion is not produced by the reduction of the nitrate ion. 

Simulated solar conversion efficiencies up to 6.8% on Ti substrates have been reported for annealed CD CdSe films in polysulphide electrolyte based on a low-ammonia-concentration-selenosulphate bath. Several successive depositions were required to build up an optimum final fihn thickness of 2.5 jim (when most of the hght was absorbed). The initial deposit was annealed to improve adherence and the final multideposited film was annealed at 550°C in air, followed by etching and zinc ion treatment. 

During the reduction, nitrite ions and polysulphides are produced. The hydrolysis reaction (17) is rather slow, if performed in a medium of alkaline hydroxides alone. It can proceed considerably more rapidly if carried out in the presence of HS ions (18). 

The concentrations of the major inorganic ions in seawater are well known in estuarine and coastal areas as well as in interstitial waters anomalies in their constant ratios may occur. The major cations are Na+, Mg2+, Ca2+, K+ and Sr2+, the major anions Cl-, SCty2-, HCO3", B(OH) ", F" and Br". Ion pairs involving these elements and H+, OH", CO32-, POif3- and SiOz -. Under anoxic conditions the S2- - ion and bi- and polysulphides become important. A summary of the major ion speciation in seawater is given by Kester et al. (1975). 

Compounds, such as the polyhalides and polysulphides, formally also the azides, could be regarded as produced by the attachment of one or more neutral non-polar halogen, sulphur or nitrogen molecules to a halogen, sulphide or nitride ion. With the last one this way of representation is definitely incorrect the azide-ion N3 is linear in contrast to the triangular structure to be expected for ionic bonding. 

The dissolution of sulphides in ammonium polysulphide can be regarded as the formation of thiosalts from anhydrous thioacids. Thus the dissolution of arsenic(III) sulphide (anhydrous thioacid) in ammonium sulphide (anhydrous thiobase), yields the formation of ammonium- and thio-arsenite ions (ammonium thioarsenite a thiosalt) ... 

AU the sulphides of the arsenic sub-group dissolve in (colourless) ammonium sulphide except tin(II) sulphide to dissolve the latter, ammonium polysulphide is needed, which acts partly as an oxidizing agent, thiostannate ions being formed ... 

Yellow ammonium sulphide (ammonium polysulphide), (NH4)2S2 dissolves the precipitate, when thioarsenate AsS ions are formed ... 

A single-crystal GaAs was used as the photoanode for the photoelectrochemical experiments. The measurements were carried out in the cell with quartz window. Cathode s and anode s areas of the cell were separated by an ion-exchange membrane. The photoanode was placed in polysulphide electrolyte 1 mol/1 Na2S +... 

In the displacement reaction (3), sulphite is not an intermediate. The reaction was studied between 250-280 °C in water and in aqueous buffer solutions . Like (1), the reaction shows first-order dependence on thiosulphate and hydrogen ion concentrations, without any indication of general acid catalysis. Minor side reactions form polysulphide and also sulphite. 

A similar mechanism is advanced for the rapid exchange between dissolved sulphur and S ions in polysulphide solutions. The fast exchange between HF and interhalogen fluorides has been accounted for by ionisation ... 

Sulphur forms more stable complexes than oxygen with these metals. In alkali metal polysulphide solutions, HgS gives the HgS - ion. The metal halides all form addition compounds with thioethers (Fig. 284). 

The formation of alkali-metal and alkaline-earth-metal sulphides and polysulphides from the elements in liquid ammonia has been extensively studied in the past, but the reactions between the metals and hydrogen sulphide in liquid ammonia have drawn detailed attention only recently. It has been suggested that the equilibrium of H2S in this solvent to give the solvated hydrosulphide ion accounts for the formation of KSH even with an excess of metal. With the alkaline-earth metals, effective preparative methods have been developed for the sulphides from H2S in liquid ammonia but anhydrous hydrosulphides have not been obtained. Now, hydrosulphides have been prepared of the form M(SH)2,xNH3 (M = Ca, Sr, or Ba x — 4, 6, or 0, respectively) from the metals with H2S in ammonia, but the compounds are stable only at low temperatures. Those of Ca and Sr are stable at —45 °C but decompose to the monosulphides at room temperature. Ba(HS)2 decomposes to BaS at 100 °C with evolution of a mole of H2S. For M (SH) (M = Rb or Cs), thermal decomposition gives polysulphides. The hydrosulphides of Rb, Cs, Sr, and Ba hydrolyse rapidly in moist air.74... 

A theoretical analysis211 indicates that the electrode process of reduction of polysulphide on a mercury electrode probably proceeds through the gradual disproportionation of S2 to a lower polysulphide and elementary sulphur, to give the final S2 ion. 

A spectroscopic study212 of solutions of alkali-metal polysulphides in DMF has shown the blue coloration to be due to the formation of the trisulphur radical anion S3. This result is contrary to that previously published (W. Giggenbach, J. C. S. Dalton, 1973, 729), which identified the species as the supersulphide ion S2. Further information on the formation of S3 in solutions of elemental sulphur in HMPA was also obtained, and it is now thought that the elemental sulphur is reduced by impurities present in the solvent, probably by dimethylamine. The reaction of piperidyl-lithium with S8 in HMPA was studied in order to determine the stoicheiometry and the nature of the final products. The stoicheiometry of the reaction was found to be ... 

The thallium(i) polysulphide TI2S5 has a structure in which the two negative charges in the 85 ion are localized at the end two S atoms. The Tl atoms are three-co-ordinate and pyramidal, so here the lone pair is sterochemically active, occupying the fourth tetrahedral position. 

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