Sulphides structure

We saw in Chapter 12 that from the structural standpoint many transition metal-oxygen systems are surprisingly complex. This is also true of many metal-sulphur systems, as we shall show later for the sulphides of Cr, Ti, V, Nb, and Ta. Before doing this we shall note some of the simpler binary sulphide structures, taking them in the order M2S, MS, MS2, M2S3 and M3S4. The chapter concludes with a short account of thio-salts and complex sulphides. 

Sulphides structurally related to zinc-blende or wurtzite... 

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... 

The origin of microbes present in hydrothermal plumes is believed to be either from a subsurface biosphere maintained by the rapid mixing processes that take place during plume formation or from entrained seawater microbes (Winn etal., 1995 Cowen etal., 1998,1999). In the latter case, most of the organisms would not be able to grow, but a small segment of the population may thrive and multiply as plumes move away from the ridge crest. Similar forms to plume bacteria are common on rock surfaces near vents and on sulphide structures (Jannasch ... 

Fluorite structure (C.N. 8 4) Rutile structure (C.N. 6 3) Silica structures (C.N. 4 2) Cadmium iodide structure Molybdenum sulphide structure Chain structure... 

Farneth et al. have investigated the mechanism of the solid-state conversion of a series of II-VI precursors of general formula (R4N )4[S4Mio(SPh)i6]" (R = Me, Et M = Gd, Zn) to the bulk metal sulphide structure. The transformation, as followed by combined TGA and mass spectroscopy, proceeds in two discrete reaction steps. In the case of cadmium derivative, the loss of countercations around 200 °G produces a new molecular solid, which was characterized (X-ray) to be GdioSi6Phi2. This intermediate composition gave a broad X-ray diffraction pattern that indicated very small (<25 A) sphalerite-phase (cubic) crystals of GdS. The second decomposition reaction eliminates S6Phi2 around 350 °G and produces phase-pure GdS (wurtzite) (Equation (5)). 

In contrast to the sulphides of most of the transition metals, sulphides of the refractory metals have quite tight stoichiometry, similar to Cr203, although, in the cases of the refractory-metal sulfides and oxides, the defects appear on the anion sub-lattice. Figure 6.1 compares the rates of oxidation and sulphidation for several of the transition and refractory metals. The low rates of sulphidation of the refractory metals are thought to be due to the low concentrations of defects in the sulphide structures. 

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