Other complex sulphides

Portionof the structure of cubanite (CuFejSs) showing slabs of the wurtzite structure with the tetrahedra pointing alternately up and down. 

The number of complex sulphide minerals is very large, and although it is possible to regard many of them as derived from simple sulphide structures (e.g. ZnS, PbS) the relationship is not always very close. For example, the Ag and Sb positions in miargyrite, AgSbS2, are close to those of alternate Pb atoms in galena (PbS), but the S atoms are so far removed from the positions of the ideal 

(a) Plan of a portion of the wurtzite structure. The metal atoms, which are all Zn atoms in wurtzite, are shown as small circles of two types to facilitate comparison with Fig. 17.17. (b) The same, with certain atoms removed, to show the relation to the layers in CuSbSa. 

Elevation of the structure ofCuSbSa, viewed parallel to the plane of the layers. The neighbours of an Sb atom in a layer are one S at 2 44 A and two S at 2-57 A. The broken lines between the layers indicate much weaker Sb-S bonds (Sb-S = 3-11 A) which account for the very good cleavage parallel to the layers. 

The atoms B (As, Sb, Bi) and C (S, Se, Te) pyramidal BC3 and/or tetrahedral BC4 groups, which does not form part of the sulpho-salt com] is the nature of the B C complex which, requirements of the A and A atoms, determines 

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In the book by Hyde and Andersson (1989), the Nowotny phases are presented as a special case of a group of ID, columnar misfit structures which also include compounds such as Bam(Fe2S4) and other complex sulphides. Layer misfit structures, such as those of some oxide-fluorides, arseno-sulphides, etc., are also presented and classified with reference to a concept of structure commensurability based on the recognition that (along one or more axes) the ratios between the different repeat units of various interpenetrating substructures can (or cannot) be represented as ratios between integer numbers. 

This can certainly be extended to other metal sulphides, using other complexes of sulphur (and also selenium). However, the complex and anion of the metal salt need to be chosen so that all the by-products of the pyrolysis reaction are volatile, otherwise the film will be contaminated with the nonvolatile by-products. For example, using cadmium nitrate and thiourea, all the by-products are volatile ... 

In (a) and (c) there would be no great difference between the characters of the A-S and B—S bonds in a particular compound, while in (b) the B and S atoms form a covalent complex which may be finite or infinite in one, two, or three dimensions. By analogy with oxides we should describe (a) and (c) as complex sulphides and (b) as thio-salts. Compounds of type (c) are not found in oxy-compounds, and moreover the criterion for isomorphous replacement is different from that applicable to complex oxides because of the more ionic character of the bonding in the latter. In ionic compounds the possibility of isomorphous replacement depends largely on ionic radius, and the chemical properties of a particular ion are of minor importance. So we find the following ions replacing one another in oxide structures Fe, Mg , Mn , Zn, in positions of octahedral coordination, while Na" " more often replaces Ca (which has approximately the same size) than K , to which it is more closely related chemically. In sulphides, on the other hand, the criterion is the formation of the same number of directed bonds, and we find atoms such as Cu, Fe, Mo, Sn, Ag, and Hg replacing Zn in zinc-blende and closely related structures. 

We have noted one difference between complex oxides and sulphides, namely, the compounds of class (c) have no counterpart among oxy-compounds. A second difference is that sulphides other than those of the most electropositive elements show more resemblance to metals than do oxides. Metal-metal bonding occurs only rarely in simple oxides whereas it is more evident in many transition-metal sulphides. In many complex sulphides of class (c), as indeed in simple sulphides such as those of Cu, it is not possible to interpret the atomic arrangements and bond lengths in terms of normal valeilce states of the metals, suggesting a partial transition to metallic bonding, as is also indicated by the physical properties of many of these compounds. 

S-Donor Ligands. TljPtjZrSg has been prepared by heating the constituent binary sulphides for 2-4 days at 400—600 °C in the absence of air. ZrC r acts with o-mercaptophenol to afford H2[Zr(o-SC6H40)3] and the i.r. spectrum of this complex has been obtained.Other complexes involving... 

The trend in architectural applications has been towards more matt finishes, and the sodium hydroxide-based etchants used frequently contain additives such as sodium nitrate or nitrite or sodium fluoride. Chelating agents such as gluconates, heptonates or sorbitol are added to complex the aluminium produced, and other additives such as sulphides may be present in the etchant to complex zinc dissolved from the alloy, and allow it to be used continuously without dumping ... 

Discussion. Minute amounts of beryllium may be readily determined spectrophotometrically by reaction under alkaline conditions with 4-nitrobenzeneazo-orcinol. The reagent is yellow in a basic medium in the presence of beryllium the colour changes to reddish-brown. The zone of optimum alkalinity is rather critical and narrow buffering with boric acid increases the reproducibility. Aluminium, up to about 240 mg per 25 mL, has little influence provided an excess of 1 mole of sodium hydroxide is added for each mole of aluminium present. Other elements which might interfere are removed by preliminary treatment with sodium hydroxide solution, but the possible co-precipitation of beryllium must be considered. Zinc interferes very slightly but can be removed by precipitation as sulphide. Copper interferes seriously, even in such small amounts as are soluble in sodium hydroxide solution. The interference of small amounts of copper, nickel, iron and calcium can be prevented by complexing with EDTA and triethanolamine. 

Sulphur dyes in the insoluble disulphide form and the Cl Solubilised Sulphur brands are reduced by the dyer as part of the application procedure. In the case of the Cl Leuco Sulphur brands reduction has already been carried out by the manufacturer, so that they are substantially in a form suitable for immediate application (section 1.6.2) The chemistry of the reduction of sulphur dyes is complex, as is the chemistry of the dyes themselves it has been well described elsewhere [204]. It is possible to describe the state of a reduced sulphur dye in alkaline sulphide or polysulphide solution by the general formula 12.42, but there are certain complications. In many cases the chromogen is not itself reduced, but in others, notably reddish browns, blues and navy blues based on indophenols, the chromogenic... 

In contrast to other sulphide-treatment flowsheets and reagent schemes, which are relatively simple, the flowsheet and reagent schemes for treatment of PGM ores can be highly complex, and varies from one ore type to the next. 

The binary phase diagrams of the titanium oxides and sulphides are very complex with the formation of a very high number of intermediate phases (a similar behaviour is observed also for other intermediate transition metals such as vanadium). In the... 

Samples of natural water should either be analysed immediately or be stored (not for a very long time) at a decreased temperature to suppress microbial processes. For the determination of nitrate and nitrite it is useful to conserve the samples by addition of 1 ml chloroform or 0.1% phenylmercuric acetate per Utre. To prevent oxidation of sulphide and some other substances in water samples, reductants are added [5, 147]. If the distribution of a species between the f ree ionic form and various complexes is to be studied, as is of ten the case, care must be taken not to shift the equiUbrium by adding substances that would enter into side reactions with the studied species. 

There are other bath compositions based on different sulphide-generating precursors and/or complexing agents. Thioacetamide and thiosulphate are two of the former, while ethylenediamine is a common example of a complexant that has been used instead of ammonia. The volatility of ammonia, and its gradual loss in an open deposition bath, is circumvented by using a less volatile complexant, such as ethylenediamine. 

This would be limited to cations that form insoluble sulphates but soluble persul-phates and thiosulphates (Ba and Sr were demonstrated by Lamer and Dinegar [30]). Thiosulphate, in particular, forms soluble complexes with many cations and therefore should (often) not present a problem in this respect, as long as the metal sulphide is not formed under the conditions of the deposition. In addition, solvents other than water can be used in principle, and therefore it might be possible to deposit sulphates that are soluble in water but insoluble in another solvent. 

Betenekov et al. [39] used an isotopic tracer technique to show that, for then-range of solution compositions, the initial deposition involved adsorption of Cd(OH)2 on the glass substrate. At the beginning of the reaction, only Cd was observed to form on the substrate and this was interpreted to be due to Cd(OH)2, since any other insoluble Cd compounds that might be formed from the deposition solution (containing CdCl2, NaOH, NH4OH, and thiourea dissolved in water) were expected to contain either S or C. However, they concluded that the deposition proceeded, not by reaction between Cd(OH)2 and sulphide formed by decomposition of thiourea, but rather by decomposition of a Cd(OH)2-thiourea complex (see Sec. 3.3.3.1). 

These factors do not argue against the complex-decomposition mechanism, but they should not be too readily interpreted, in the absence of other evidence, as evidence against the sulphide mechanism. Granted, this is an old study, but it does point up the difficulty in distinguishing between the two mechanisms. Kinetic studies and subsequent fitting of the data from these studies to various models [48,49] appear to be the best way of approaching this problem at present. 

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