Aqueous solution chemistry and complexes

Phosphorus sulhdes ignite easily, and P4S3 is used in strike anywhere matches it is combined with KCIO3, and the compounds inflame when subjected to friction. Whereas P4S3 does not react with water, other phosphorus sulfides are slowly hydrolysed (e.g. reaction 15.150). 

The only well-characterized binary sulfide of Sb is the naturally occurring Sb2S3 (stibnite), which has a doublechain structure in which each Sb(III) is pyramidally sited with respect to three S atoms. The sulfide can be made by direct combination of the elements. A metastable red form can be precipitated from aqueous solution, but reverts to the stable black form on heating. Like AS2S3, Sb2S3 dissolves in alkali metal sulfide solutions (see equation 15.152). Bismuth(III) sulfide, 61283, is isostructural with 86283, but in contrast to its As and 8b analogues, 61283 does not dissolve in alkali metal sulfide solutions. 

When P285 is heated under vacuum with CS28 and sulfur in a 1 2 7 molar ratio, CS4P2S10 is formed. This contains discrete [62810] - ions (15.78), the terminal P—S bonds in which are shorter (201 pm) than the two in the central chain (219 pm). 

Arsenic and antimony sulfide ores are major sources of the group 15 elements (see Section 15.2). In the laboratory, AS283 and AS285 are usually precipitated from aqueous solutions of arsenite or arsenate. Reaction 15.151 proceeds when the H28 is passed slowly through the solution at 298 K. If the temperature is lowered to 273 K and the rate of flow of H28 is increased, the product is AS285. 

Many aspects of the aqueous solution chemistry of the group 15 elements have already been covered  

In this section we focus on the formation of aqueous solution species by Sb(III) and 6i(III). Solutions of Sb(III) 

The following terms were introduced in this chapter. Do you know what they mean  

Corbridge (1995) Phosphorus, 5th edn, Elsevier, Amsterdam - A book covering of all aspects of phosphorus chemistry. 

Emsley (2000) The Shocking Story of Phosphorus, Macmillan, London - A readable book described as a biography of the devil s element . 

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Aluminium to thallium salts of oxoacids, aqueous solution chemistry and complexes... 

Oxidation-reduction potentials for complexes in solution are determined by the relative stabilities of the complexes of the metal ion in the lower and higher oxidation states. The thermodynamic cycle connecting redox potentials and stabifity constants is shown in Fig. 7. This cycle can be useful both in rationalizing aspects of aqueous solution chemistry of complexes and in predicting or estimating values for stabifity constants or redox potentials for systems which are difficult or impossible to access experimentally. Thus knowledge of stabifity... 

This interface is critically important in many applications, as well as in biological systems. For example, the movement of pollutants tln-ough the enviromnent involves a series of chemical reactions of aqueous groundwater solutions with mineral surfaces. Although the liquid-solid interface has been studied for many years, it is only recently that the tools have been developed for interrogating this interface at the atomic level. This interface is particularly complex, as the interactions of ions dissolved in solution with a surface are affected not only by the surface structure, but also by the solution chemistry and by the effects of the electrical double layer [31]. It has been found, for example, that some surface reconstructions present in UHV persist under solution, while others do not. 

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

The aqueous solution chemistry of Ir in its higher oxidation states III, IV, and V has been explored by Sykes et al.41,48 Chemical and electrochemical oxidation of Ir(H20)6]3+ gives a brown-green Irv product, which undergoes chemical and electrochemical reduction to a blue and a purple IrIV complex. 170 NMR studies are consistent with double- and single-bridged dimeric structures, with likely formulas [(H20)4Ir(/i-0H)2Ir(H20)4]6+ for the blue complex and [(H20)5Ir(/r-0)Ir(H20)5]6+ for the purple one. 

The aqueous solution chemistry of Tc(VII) is dominated by the stability of the TeO anion [4], Nitrido complexes are few and are limited to peroxides and one dimeric nitrido-hydrazido example. The peroxo complexes based on the [TcVIIN(02 )2] core are analogous to the well-known isoelectronic [MoviO(02)2] complexes [117] and are the only examples of nitridoperoxo complexes and rare examples of peroxo complexes of a metal in the +7 oxidation state. 

As geochemists, we frequently need to describe the chemical states of natural waters, including how dissolved mass is distributed among aqueous species, and to understand how such waters will react with minerals, gases, and fluids of the Earth s crust and hydrosphere. We can readily undertake such tasks when they involve simple chemical systems, in which the relatively few reactions likely to occur can be anticipated through experience and evaluated by hand calculation. As we encounter more complex problems, we must rely increasingly on quantitative models of solution chemistry and irreversible reaction to find solutions. 

Pyridinecarboxaldehyde, 3. Possible hydration of the aldehyde group makes the aqueous solution chemistry of 3 potentially more complex and interesting than the other compounds. Hydration is less extensive with 3 than 4-pyridinecarboxaldehyde but upon protonation, about 80% will exist as the hydrate (gem-diol). The calculated distribution of species as a function of pH is given in Figure 4 based on the equilibrium constants determined by Laviron (9). 

Given the structure of InF3-3H20 (see above) and the tendency of indium(III) to be six-coordinate with hard ligands, it is reasonable that the mixed fluoro/aqua anionic complexes should also be [InF4(H20)2] and [InF5(H20)]2. This is compatible with the evidence from aqueous solution chemistry, where stability constants and thermochemical results indicate a series of [In(H20)6-nFn]l3 n)+ species.9 These complexes still await detailed systematic structural investigation. 

Chromium(IV) does not have any aqueous solution chemistry except for the formation of intermediates in the reduction of CrVI to Crm. Chromium(IV) compounds tend to disproportionate into Cr111 and CrVI species (equation 78) and the metal ion in this oxidation state is powerfully oxidizing towards organic compounds. An eight-coordinate complex [CrH4(dmpe)4] is known (Section 35.3.4.1). 

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