Polyselenide ions

The results for H2Se(aq) and HSe are selected. The value of AfG°(Se P 298.15 K) is compatible with the corresponding value independently evaluated from redox potentials of mono- and polyselenide ions in Section V.3.4.3, (127.9 1.9) kJ-moP. The finally selected value is chosen as the mean of these values... 

Only one study has been published on the protonation of polyselenide ions. Schoneshofer, Karmann, and Henglein [69SCH/KAR] exposed H2Se(aq) to radiolysis with 1.5 MeV electrons and identified H2Se2 as the end product of a series of radical reactions. The acidity constants of this compound were determined from spectropho-tometric measurements, but as no information coneerning the pH determination is provided, the protonation constants reported, logn, log g = 9.3, are of... 

The Figure depicts an experiment in which an increasing amount of Se(0) is added to a 10 M solution of HSe / Se . Up to a total concentration of Se(0) of 2.8 X 10 mol-dm, all of the elemental selenium added is incorporated into polyselenide ions. At larger Se(0) additions, an increasing fraction of the addition remains as Se(cr) and [Se(0)],o, then represents a hypothetical concentration. The diagram shows that Sej and Se predominate in solutions saturated with Se(cr). Hence, the calculated value of A (V.36) is practically independent of the protonation constant of the Se ion. 

The potentiometric titration data (295 K , pH-buffer scale) were all collected at an analytical composition of the solution very close to HSe, which make them highly vulnerable to experimental errors. The evaluated value of pA a2, 11.7, is also claimed to be much too low because of the formation of polyselenide ions . 

The diselenaborane was obtained as an unexpected minor product during the reaction of decaborane(14) with polyselenide ion in aqueous base. The major product was the [BjqHj jSe] ion. It was reported previously that aqueous base degraded BjoHj to form the [B9H14]" ion. Subsequent study proved that polyselenide ion reacted rapidly with [BqHjJ" to form B HsSej in good yield. The procedure for the preparation of this diselenaborane in two steps from decaborane(14) is described here. 

Reaction of with the polyselenide ion formed B MgSej in good... 

RAY/D1C] Raymond, C. C., Dick, D. L., Dorhout, P. K., Speciation of main-group metal ions by electrospray mass spectrometry. 1. Investigation of aqueous polyselenide species and effects of cations and pH, Inorg. Chem., 36, (1997), 2678-2681. Cited on page 154. 

Structurally, the smaller polyselenide and polytelluride ions resemble their polysulfide analogues, e.g. [Teg] has structure... 

In this section, we review the characterization of photoetching patterns evolved on the surface of polycrystalUne CdX(X = S, Se), which are one of the most extensively studied semiconductors as photoelectrodes in photoelectrochemical cells, photoconductors, and other optoelectronic usages. Anodic photocurrent flowing through the electrode-electrolyte interface is entirely due to the oxidative dissolution of the semiconductors themselves to form Cd " " ion and elemental chalco-gen, except in certain redox solutions, such as aqueous polysulfide, polyselenide, and alkanolamine solutions. For example, in an aqueous NaCl solution, CdSe is photoanodically decomposed to form Cd + ion and elemental Se. After the photoelectrolysis of a CdSe electrode under potentiostatic conditions and a subsequent... 

In contrast to the polysulfides and almost all the polyselenides (exception Cs4Sei6 ), a number of polytelluride anions are also known with total negative charges greater than 2, as, for instance, in NaTe with discrete [Tcs]" ions and in 83X022 with polymeric sheet-Uke [Tcg ] ions. These are examples for the striking variety of structural motifs and formula types (x/y = 5/3, 1/1, 2/3, 2/5, 1/3, 1/4, 1/6, 2/13, 1/7 and 3/22) that are known for the alkali metal polytellurides A TCj, and which reflect the propensity of tellurium both to catenate and to participate in hypervalent coordination polyhedra. Whereas discrete anions are observed for xjy > 2/3, polymeric chain and lamellar anionic networks are present in such tellurides when xfy < 2/5. ... 

The [AuSeialn chain is the most Se-rich Au compound to date and it is another remarkable example of a monodentate polyselenide (8652-), where one terminal Se is coordinated to a transition metal while the other is ionically interacting with an alkali ion. 

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