Cobalt hexacyanide

Analysis of the halohydrocarbons, halocarbons, and sulfur hexafluoride is usually achieved by gas chromatography that is equipped with an electron capture detector. Complex metal anions, such as cobalt hexacyanide, are used as nonradioactive tracers in reservoir studies. The cobalt in the tracer compound must be in the complex anion portion of the molecule, because cationic cobalt tends to react with materials in the reservoir, leading to inaccurate analytic information [1226]. 

The cobalt-hexacyanide spectrum, which has two well-resolved major... 

When the rates at which Hj reacts with aqueous mixtures of CoCL and KCN at 1° are determined as a function of the mole ratio R (CN/Co), it is found that there are two maxima, the first at 12 = 3.9 and the second at R > 100. The homogeneous reaction which occurs at i2 > 5 is catalyzed by the small amount of cobaltous hexacyanide ion that is in equilibrium with colbaltous pentacyanide ion. 

The reaction kinetics at R > 5 provides substantial evidence, although indirect, that cobaltous hexacyanide ion can exist in small concentration and is responsible for the H2 uptake observed in solutions free of precipitate. 

The complexation of coordination compounds may make it possible to control their photochemical behaviour via the structure of the supramolecular species formed. For instance, the binding of cobalt(m) hexacyanide by macrocyclic polyammonium receptors markedly affects their photoaquation quantum yield in a structure-dependent manner [8.73-8.77]. It thus appears possible to orient the photosubstitution reactions of transition-metal complexes by using appropriate receptor molecules. Such effects may be general, applying to complex cations as well as to complex anions [2.114]. 

Rollier, M. A. and E. Arreghini Structure of Copper Salts of Some Complex Cyanides I. Structure of Copper Salts of the Hexacyanides of Cobalt and Chromium. Gazz. chim. Ital. 69, 499 (1939). 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

Potentiometric and glass electrode titrations of KCN solution against C0CI2 suggest that a definite chemical compound containing cyanide and cobalt in the empirical ratio 9/2 can be formed in the mixtures. Kinetic evidence is used to show that when R is small, the hydrogenation catalyst is either a dimer of this composition, adsorbed on insoluble cobaltous dicyanide, or alternatively that it is adsorbed hexacyanide ion. The latter hypothesis receives most support. 

At low values of R (the mole ratio of total cyanide to total cobalt) there is a precipitate of pink cobaltous dicyanide which dissolves as more KCN is added. At E = 5 (under most experimental conditions) a clear solution is obtained that may be straw-colored, or greenish-yellow. The work of Hume and Kolthoff (3) and of Adamson (4) shows that this is a solution of cobaltous pentacyanide ion and suggests that Co does not form a hexacyanide. Adamson (4) finds that pentacyanide ion in solution is paramagnetic and largely or entirely in the monomeric form [Co (CN)6] . 

Figure 3 shows the result of experiments conducted at different total cobalt concentrations [Co], R being kept constant at 4.2. The best straight line is obtained when the rates are plotted as a function of [Co], in accord with the expression given in Table I for case 11, which supposes that the catalyst is adsorbed hexacyanide ion. 

Dissolve 4 g of potassium cobalt (III) hexacyanide (KjCo(CN) ) and 1 g of potassium chlorate in 100 mL of water. Soak filter paper in solution and dry at 100 °C. Apply a drop of the zinc solution and heat in an evaporating dish. A green disk on the filter paper is obtained if zinc is present. 

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