Chalconides, metal

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

Class la. We can envisage systems of bonded metal atoms which are then cross-linked by ligands X, there being no metal-metal interactions between the different sub-units. Examples include Gd2Cl3, Ta2S, and Ta S further examples are likely to emerge from studies of sub-halides, sub-chalconides, etc. 

Table 7.10 shows the c.n. s of A in simple AX structures. The structures are divided into two groups which we shall describe as (a) normal and (b) polarized ionic structures. The former are typically those of fluorides and oxides (with the exception that the NaQ structure is adopted more generally by all halides of most of the alkali metals and by all chalconides of the alkaline-earths), while the... 

We saw in Chapter 4 that from the geometrical standpoint the structures of many inorganic compounds, particularly halides and chalconides, may be regarded as assemblies of close-packed non-metal atoms (ions) in which the metal atoms occupy... 

Most metallic elements react directly with S, Se, Te and, so far as is known, Po. Often they react very readily, mercury and sulfur, for example, at room temperature. Binary compounds of great variety and complexity of structure can be obtained. The nature of the products usually also depends on the ratios of reactants, the temperature of reaction, and other conditions. Many elements form several compounds and sometimes long series of compounds with a given chalconide. We shall give here only the briefest account... 

Here, IF5 serves both as the fluorinating agent and the solvent. In these complexes there is considerable interionic electron spin coupling which makes them antiferromagnetic (Neel temperatures of the order of 100— 150°K). These couplings must take place by overlap of orbitals of the fluoride ions of adjacent [MF6] units in the crystals, that is, by a superexchange process similar in principle to that in halides and chalconides of some divalent metals of the first transition series. Such an explanation, of course, requires the assumption of significant overlap of metal r/rc (t23) orbitals with fluoride ion pn orbitals. 

Typical coprecipitation synthetic methods involve the following stages (i) nanomaterials formation takes place from aqueous solutions, or by reduction from non-aqueous solutions, electrochemical reduction and decomposition of metal-organic precursors with templates (ii) metal chalconides are formed by the reactions of molecular precursors (iii) microwave/sonication assists the coprecipitation to take place at the microscale with the following advantages ... 

The catalysts applied to alkene epoxidation in fluorinated alcohol solvents can be subdivided into those which are metal/chalconide-based and those which are purely organic in nature (Scheme 4.5). The former comprise arsanes/arsane oxides [27,28], arsonic acids [29, 30], seleninic acids/diselenides ]31-35], and rhenium compounds such as Re207 and MTO (methylrhenium trioxide) ]36,37]. As shown in Scheme 4.5, their catalytic activity is ascribed to the intermediate formation of, for example, perseleninic/perarsonic adds or bisperoxorhenium complexes. In other words, their catalytic effect is due to the equilibrium transformation of hydrogen peroxide to kmetically more active peroxidic spedes. 

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