Cobalt ion complexes

Chemically Activated Species with Well Characterized Internal Energies. Atomic cobalt ions react with isobutane to yield two products as indicated in reactions 7 and 8, which involve the elimination of hydrogen and methane to yield cobalt ion complexes with isobutylene and propylene, respectively(S). 

The retention and DFs for cobalt ions were low when UF membranes were applied (Figure 25.7). To intensify the effect of separation, the complexing agents PAA of different cross-linking, PAA salts, PEI, and INSTAR AS (complexing agent containing macromolecular AAm and sodium acrylate copolymer) were added to the feed solution. The results of UF of cobalt ions complexed before filtration by... 

Metal ion complexation rates have been studied by the T-jump method. ° Divalent nickel and cobalt have coordination numbers of 6, so they can form complexes ML with monodentate ligands L with n = 1—6 or with bidentate ligands, n = 1-3. The ligands are Bronsted bases, and only the conjugate base form undergoes coordination with the metal ion. The complex formation reaction is then... 

It is possible to observe spin-allowed, d d bands in the visible region of the. spectra of low-spin cobalt(lll) complexes because of the small value of 0Dq, (A), which is required to induce spin-pairing in the cobalt(lll) ion. This means that the low-spin configuration occurs in complexes with ligands which do not cause the low -energy charge transfer bands whieh so often dominate the spectra of low-spin complexes. 

When, however, the ligand molecule or ion has two atoms, each of which has a lone pair of electrons, then the molecule has two donor atoms and it may be possible to form two coordinate bonds with the same metal ion such a ligand is said to be bidentate and may be exemplified by consideration of the tris(ethylenediamine)cobalt(III) complex, [Co(en)3]3+. In this six-coordinate octahedral complex of cobalt(III), each of the bidentate ethylenediamine molecules is bound to the metal ion through the lone pair electrons of the two nitrogen atoms. This results in the formation of three five-membered rings, each including the metal ion the process of ring formation is called chelation. 

Discussion. An excellent method for the colorimetric determination of minute amounts of cobalt is based upon the soluble red complex salt formed when cobalt ions react with an aqueous solution of nitroso-R-salt (sodium 1-nitroso-2-hydroxynaphthalene-3,6-disulphonate). Three moles of the reagent combine with 1 mole of cobalt. 

As already mentioned, complexes of chromium(iii), cobalt(iii), rhodium(iii) and iridium(iii) are particularly inert, with substitution reactions often taking many hours or days under relatively forcing conditions. The majority of kinetic studies on the reactions of transition-metal complexes have been performed on complexes of these metal ions. This is for two reasons. Firstly, the rates of reactions are comparable to those in organic chemistry, and the techniques which have been developed for the investigation of such reactions are readily available and appropriate. The time scales of minutes to days are compatible with relatively slow spectroscopic techniques. The second reason is associated with the kinetic inertness of the products. If the products are non-labile, valuable stereochemical information about the course of the substitution reaction may be obtained. Much is known about the stereochemistry of ligand substitution reactions of cobalt(iii) complexes, from which certain inferences about the nature of the intermediates or transition states involved may be drawn. This is also the case for substitution reactions of square-planar complexes of platinum(ii), where study has led to the development of rules to predict the stereochemical course of reactions at this centre. 

Cobalt(III) complexes containing mixed chelating ligands have been produced. Reaction of potassium bis[biuretocobaltate(III)], K2[Co(bi)2] with R2dtc or Rxant at 0° produces (313) the blue-violet [Co(bi)2(S—S)] ion (S—S = R2dtc or RXant). If the reaction is performed above 0° in the presence of water, the products are [Co(bi)2(S—S>2] and biuret. 

Sometimes, the physicochemical properties of ionic species solubilized in the aqueous core of reversed micelles are different from those in bulk water. Changes in the electronic absorption spectra of ionic species (1 , Co ", Cu " ) entrapped in AOT-reversed micelles have been observed, attributed to changes in the amount of water available for solvation [2,92,134], In particular, it has been observed that at low water concentrations cobalt ions are solubihzed in the micellar core as a tetrahedral complex, whereas with increasing water concentration there is a gradual conversion to an octahedral complex [135],... 

During oxidation of tin(II) ions by hydrogen peroxide, iodine, bromine, mercury(ir) and thallium(III) the induced reduction of cobalt(in) complexes cannot be observed. Therefore, it was concluded that these reactions proceed by 2-equivalent changes in the oxidation states of the reactants. 

Methyl-5-amino-l-formylisoquinoline thiosemicarbazone, 22, also yields cobalt(II) complexes from unheated methanol solution [202]. However, due to this ligand s added steric requirements, a complex, [Co(22)Cl2], with one ligand per metal ion center is formed. This brown solid has a magnetic moment of 4.42 B.M., is a non-electrolyte, has coordination of a neutral NNS ligand, and the electronic spectrum indicates approximate trigonal bipyramidal stereochemistry. 

Bond length differences between HS and LS isomers have been determined for a number of iron(II), iron(III) and cobalt(II) complexes on the basis of multiple temperature X-ray diffraction structure studies [6]. The available results have been collected in Table 17. Average values for the bond length changes characteristic for a particular transition-metal ion have been extracted from these data and are obtained as AR 0.17 A for iron(II) complexes, AR 0.13 A for iron(III) complexes, and AR = 0.06 A for cobalt(II) complexes. These values may be compared with the differences of ionic radii between the HS and LS forms of iron(II), iron(III) and cobalt(II) which were estimated some time ago [184] as 0.16, 0.095, and 0.085 A, respectively. 

The given structure shows two molecules of TTA to have reacted with a cobalt ion to form the cobalt-TTA complex, in which the cobalt atom forms a valence bond solid lines) with one, and a coordinate bond (broken lines) with the other, oxygen atom of each TTA molecule. Thus, in the cobalt-TTA complex there is a six-membered ring formed by each TTA molecule with the cobalt atom. Metal chelate complexes of this type have good stability, they are nonpolar and soluble in the organic phase. The usefulness of the chelating extractants in solvent extraction is therefore obvious. 

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