Sulphides and Selenides

Sulphides and Selenides. The new compounds VySg and VySeg have been prepared and shown to have NiAs-type structures with ordered vacancies. 

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A"-Ray structure determinations (see Chapter 11 for details) have been reported for triphenylphosphine oxide, tri-o-tolylphosphine oxide, sulphide, and selenide, and for cw-2,2,3,4,4-pentamethyl-l-phenylphos-phetan-1-oxide (5). Electron spectroscopic studies of phosphorus oxychloride and thiophosphoryl chloride in the gaseous state, and n.m.r., i.r., and u.v. spectra of phosphine sulphides have appeared. Dipole moments have been used to define the stereochemistry of 2-cyanoethylphosphine oxides, such as (6), which is shown in its preferred conformation. 

Restricted rotation has been observed in tris-o-tolylphosphine sulphide and selenide (39). The spectrum of the selenide shows two methyl environments in the ratio 2 1 at 30 °C but the methyl signals of the sulphide resolved to this pattern only upon cooling the sample. The corresponding oxide and the parent phosphine showed only one methyl environment down to — 60 °C. Y-Ray diffraction of the selenide showed that the methyl group on one aryl group is directly behind the phosphorus atom in the crystal, as shown in (39). 

Two heterocyclic systems have been investigated - the 1,3,2-dioxaphosphepene (45) and its oxide,13 1,3,2-dioxa-phosphorinanes and their oxides, sulphides and selenides (46).136,137 Three ring vibrations were involved in the conformational study of the amides (46, Y = NR2).137... 

X-Ray.—The crystal and molecular structure of tri-o-tolylphosphine, its oxide, sulphide, and selenide (125) have been compared. The mean P—C bond lengths appear to be determined by the n-electron density along the P—C bond and intramolecular steric interactions, d-Orbital participation was considered to be of little importance.152 X-Ray diffraction established the structure of diphosphinofumarate (126)153 and showed that the phospholanium iodide (127) has an envelope ring with the methyl group at the point of the flap.154 The bicyclic phosphonium bromide (128) has a distorted half-chair phosphorus-containing ring, one of the P—C bonds in the... 

The following compounds are unaffected by bis(p-methoxyphenyl) telluroxide dithi-olanes, enamines, aldehydes, ketones, alcohols, pyrroles, indoles, amino acids, aromatic amines, monohydroxyarenes, esters, hindered thiocarbonates, isonitriles, oximes, arylhy-drazones, sulphides, and selenides. ... 

The title compounds are prepared respectively from phenyl-2-aminophenyl sulphide and selenide in accordance with the accompanying scheme. 

The reaction of triphenylphosphole, its oxide, sulphide, and selenide with Fe" has been studied. The phosphole reduces Fe". " ... 

Goodall (53) has synthesised a series of sulphur and selenium containing ligands related to the ligands used by Kouwenhoven. These are the sulphide and selenide ligands shown in Fig. 39. 

The essential difference is that aU the other methods give isoelectric anions considerably larger than cations, while the Electron Density Minimum method does not. Yet, for example, the mineralogy of oxides and silicates suggests large oxide anions often in contact (47) and there is evidence for anion-anion contact in sulphides and selenides (2). This evidence for anion-anion contact is the strongest evidence for the older systems of ionic radii. 

The next five chapters deal with deposition of specific groups of semiconductors. In Chapter 4, II-VI Semiconductors, all the sulphides, selenides, and (what little there is on) tellurides of cadmium (most of the chapter), zinc (a substantial part), and mercury (a small part). (Oxides are left to a later chapter.) This chapter is, understandably, a large one, due mainly to the large amount of work carried out on CdS and to a lesser extent on CdSe. Chapter 5, PbS and PbSe, provides a separate forum for PbS and PbSe, which provided much of the focus for CD in earlier years. The remaining sulphides and selenides are covered in Chapter 6, Other Sulphides and Selenides. There are many of these compounds, thus, this is a correspondingly large chapter. Chapter 7, Oxides and Other Semiconductors, is devoted mainly to oxides and some hydroxides, as well as to miscellaneous semiconductors that have only been scantily studied (elemental selenium and silver halides). These previous chapters have been limited to binary semiconductors, made up of two elements (with the exception of elemental Se). Chapter 8, Ternary Semiconductors, extends this list to semiconductors composed of three elements, whether two different metals (most of the studies) or two different chalcogens. 

A large range of other metal sulphides and selenides have been deposited by CD. Since these will be individually described in Chapter 6, it will be sufficient here to list all binary sulphides and selenides (along with oxides) in Table 2.1, along with up to three references to each compound. 

There is one example of a CD process (for deposition of tin sulphides) in which elemental sulphur dissolved in a nonaqueous solvent is used as a source for S. Since this appears to be the only example in the literature for this type of film deposition, it will be discussed in Chapter 6 together with the relevant study on tin sulphides. However, there is no reason to believe that this process may not be applicable to other materials. Metal sulphides (and selenides) are known to form, as precipitates, by reacting certain metal salts with dissolved elemental chalcogen, although visible film formation seems to be limited, up to now, to this one example. 

This chapter covers sulphides and selenides not included in Chapters 4 and 5, i.e., all metals except for Zn, Cd, Hg, and Pb. Some of these materials, e.g., the sulphides of Bi, Cu, and Ag and Cu-Se, have been the subject of many investigations. There are others, however, on which as little as one paper has been published altogether. 

The few cases reported for CD sulphides and selenides of T1 all reported the monosulphide (selenide)—TIS or TlSe. T1 can be monovalent or trivalent, and these apparently divalent compounds are believed to be mixed-valence compounds, with both T1(I) and Tl(III) present. 

Considering that homogeneous precipitation of metal chalcogenides (mainly sulphides) by reaction between metal ions and dissolved chalcogen is well established, the main difference between this deposition and similar reactions seems to be that the products adhere to a substrate to give a visible fdm (in this case) rather than only precipitate. Whether this is connected with the redissolu-tion/redeposition process that occurs with the Sn-S system or has some other explanation is important. If the former, it may be limited to only those systems that behave similarly. Otherwise it is not unreasonable to expect that other metal sulphides and selenides (possibly also tellurides, although tellurium tends to be much less soluble, if at all, in such solvents) may be deposited as films in this manner. 

Most of the compounds deposited by CD have been sulphides and selenides. Apart from a very few examples of tellurides (and some related teUuride experiments) and with a very few exceptions, discussed at the end of this chapter, what is left is confined to oxides (including hydrated oxides and hydroxides and two examples of basic carbonates.) This chapter deals mainly with these oxides. In addition, as noted in Chapter 3, there are a nnmber of slow precipitations that resnlt in precipitates, rather than films, of varions other componnds, not necessarily semiconductors in the conventional sense. These potential CD reactions, briefly discnssed in Chapter 3, will be somewhat expanded on in this chapter. 

Bandgap measurements for Cu sulphides and selenides are complicated by the fact that these semiconductors are normally degenerate, with high free-carrier absorption in the near-infrared and possible Moss-Burstein shifts (due to saturation of the top of the valence band by holes) in the optical gap. It is quite possible that variations in bandgaps in these materials are due to differences in stoichiometry, phase, and doping rather than to any quantum size effect. Only studies where crystal size can be estimated and are possibly in the quantum size range are given here. 

Transitional-metal sulphides and selenides with pyrite structure of the form MS2 and MSe2 Ni(Sej —xSx)2... 

The hindered silyl chlorides (Ar X)3SiCl (X = S, Se) react with AgCICU to give a range of sulphides and selenides which are thought to result through the intermediacy of the silicenium ion which loses Ar X+ and (Ar X)2Si (X = S) or Ar X (X = Se). With the thio derivative, the products are the disulphide (5), sulphide (6) and arene (equation 13), while for the selenium chloride, diselenides and selenides dominate (equation 14)25. 

Sulphonium ylides are in certain cases unstable and they undergo further transformation affording useful final products. In this way allylic sulphides and selenides were used to transfer an alkylthio- or alkylseleno-group onto the a-carbon of / -dicarbonyl compounds in the form of their ylides the sequence of reactions were a transylidation followed by [2,3]-sigmatropic rearrangement. 

Folmer, J. C. W., and F. Jellinek (1980). The valence of copper in sulphides and selenides an x-ray photoelectron spectroscopy study. J. Less Common Metals 76, 153-62. 

In 1970 Jamison and Cosgrove reported an interesting study of the relationship between the crystal structure and the lubrication performance of the sulphides and selenides of several of the transition metals in Groups 4, 5, 6 and 7 of the Periodic Table (see Table 14.2). They showed experimentally that satisfactory film formation and low friction were only obtained within certain closely-defined limits of crystal structure. It is not proposed here to attempt to present full details of the rather complex crystallographic considerations, but only to give a simplified version of the essential aspects of their findings. 

Once an electron has been received the uninegative ion repels further electrons hence the negative affinities displayed by oxide, sulphide and selenide 2-negative ions. 

Figure 4.26. The three possible tetrahedral Si configurations in chalcogenide glasses and the corresponding Si chemical shifts in sulphide and selenide glasses. Adapted from Moran et al.

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