Chalcogenides formation

The initial step of the reaction, Eq. (7), provides the individual metal sulfide molecules via reaction of the M2+ ions with H2S. In the case of films derived from fatty acids, the two carboxylate functions, associated with the M2+ ion, are the sink for the two protons released from the reaction. The diffusion and coalescence of the individual MS molecules to give MS particles are depicted in Eq. (8). Despite an abundance of literature concerning Q-state particle formation in LB films, there has been little discussion relating to mechanistic aspects of how the nature of the LB support matrix effects the processes depicted in Eq. (7) and (8). The remainder of this section outlines the mechanistic and kinetic insights gained into these processes over the course of study of metal chalcogenide formation in LB films. 

Aqueous solutions have low conductivities resulting from extensive complex ion formation. The haUdes, along with the chalcogenides, are sometimes used in pyrotechnics to give blue flames and as catalysts for a number of organic reactions. 

The oxide (p. 1209), chalcogenides (p. 1210) and halides (p. 1211) have already been described. Of them, the only ionic compound is HgF2 but other compounds in which there is appreciable charge separation are the hydrated salts of strong oxoacids, e.g. the nitrate, perchlorate, and sulfate. In aqueous solution such salts are extensively hydrolysed (HgO is only very weakly basic) and they require acidification to prevent the formation of polynuclear hydroxo-bridged species or the precipitation of basic salts such as Hg(OH)(N03) which contains infinite zigzag chains ... 

Due to the high heats of formation of the binary components, these small values seem to be representative for most of the chalcogenide halides discussed in this article. 

The compounds HgaY2X2 (Y = S, Se, Te X = Cl, Br, I) are insoluble in water, dilute acids, and cone. HCl, and they are not attacked by these solvents. Cone. HNO3 converts the sulfide chloride into the sulfide nitrate HgsSalNOsla (20, 290). With bases, rapid decomposition occurs, leading to the formation of oxide chacogenides (20), or a mixture of oxide and chalcogenide (111), a matter on which agreement has not yet been reached. 

Just as, in Group VB, niobium, so, in this Group, molybdenum provides most of the examples of the chalcogenide halides. The occurrence and preparation of such compounds are described in numerous publications. In most cases, they have been obtained as powders, with the composition based on chemical analyses only. The presence of defined, homogeneous phases is, therefore, in many cases doubtful. In addition, some published results are contradictory. A decision is possible where a complete structure analysis has been made. As will be shown later, the formation of metal-metal bonds (so-called clusters), as in the case of niobium, is the most characteristic building-principle. Such clusters... 

Preparative Routes and Experimental Conditions for the Formation OF Rhenium Chalcogenide Halides... 

Treatment of the rhenium sulfide chlorides with an excess of chlorine at temperatures above 450°C results in formation of ReCls 140). Reduction between 350 and 500°C gives binary rhenium chalcogenides 139,262). Action of water vapor on rhenium sulfide chlorides at 350-500°C produces oxysulfides 139). 

It was found that the region of formation of the chalcogenide halides depends on the pH, the solvent concentration, and the ratios of the initial components in the charge. Temperature and pressure have practically no influence on the phase formation in these systems (285). The use of bromine (283) and SeBr2 as the solvent leads to a different mechanism, having different kinetics of formation and different growth-forms of the crystals (285). 

In the presence of a metal ion (M " ), a metal chalcogenide phase M2Sen will be precipitated upon exceeding the solubility product of [M and [Se ] (or [HSe ]). The concentration of free metal ions must be controlled by an excess of complexing agent, determining the applicable solubility of the metal and the overall competitive chemical reaction, in order to prevent the formation of sulfite, sulfate, and... 

Froment M, Lincot D (1995) Phase formation processes in solution at the atomic level Metal chalcogenide semiconductors. Electrochim Acta 40 1293-1303... 

The racemization of the phosphine (118) has been followed by optical rotation. The lack of a solvent effect indicates that there is little change in dipole moment in the formation of the planar transition state. Circular dichroism has been used to study the interactions of nucleotides with proteins and DNA with a histone. Faraday effects have been reviewed. Refraction studies on chloro-amino-phosphines, fluoro-amino-phosphines, and some chalcogenides are reported. 

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