Cobalt divalent state

The formation of the triammino-salt indicates that two of the cobalt atoms are united with three molecules of ammonia, and the evolution of chlorine shows that one cobalt atom has been reduced from trivalent to divalent state. The reaction may be represented thus ... 

Cobalt. The speciation of radiocobalt has been selected for discussion in this chapter because it exemplifies an element for which much information already exists regarding its stable chemical speciation, yet there are additional species which have become environmentally important as a result of the activities of the nuclear industry Cobalt, the middle member of the first triad of group VIII transition metals in the Periodic Table (iron, cobalt, nickel), is most stable in the divalent state when in simple compounds. Studies of radionuclide releases from nuclear power plants under tropical conditions in India seem to indicate that... 

C in hydrogen was needed to get all cobalt ions of CoAPOs in divalent state hereafter named reduced catalysts... 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

Reduction lowers the charge to radius ratio of transition metal ions, promoting higher rates of ligand substitution. Reduced, divalent oxidation states of manganese, iron, cobalt, and nickel are also quite soluble (Table II). 

Cobalt and nickel are Group VlllA and copper Group IB elements. They occur predominantly in the +2 oxidation state in soils as divalent cations, though Co + may be oxidized to Co forming very insoluble compounds with Mn oxides, and... 

Spectra of the mixed spinels are interpretable in terms of X-ray diffraction studies of the same samples by Azdroff (16). Cobalt appears to be in the divalent condition, based upon the location of the principal maximum. Manganese appears in a higher valence state. The extended fine structure, which is supposed to be determined by the lattice, appears identical for all the spectra of Figs. 14 and 15 which are of truly cubic spinels, namely CosOi,... 

Cobalt in its trivalent state forms many stable complexes in solution. In these complexes, the coordination number of Co + is six. The Co2+ ion also forms complexes where the coordination number is four. Several complexes of both the trivalent and divalent ions with ammonia, amines, ethylene diamine, cyanide, halogens and sulfur ligands are known (see also Cobalt Complexes). 

Cobalt forms many complexes in both the divalent and trivalent states. While the d Co2+ ion exhibits a coordination number of four or six in the trivalent state, the d Co3 ion mostly exhibits coordination number six. Also, trivalent cobalt forms more stable complexes than Co2+ ion, and there are many more of them. The most common donor atom in cobalt complexes is nitrogen. 

Now it is very remarkable that cobalt, in ionic compounds, is unstable in the tervalent state, and that the divalent ion has no reducing properties. In a covalent complex ion, cobalt must be in the tervalent state in order to be able to form an 18-electron configuration. By the complex formation, the tervalent state, unusual in ionic compounds, is stabilized. 

In terms of the development of an understanding of the reactivity patterns of inorganic complexes, the two metals which have been pivotal are platinum and cobalt. This importance is to a large part a consequence of each metal having available one or more oxidation states which are kinetically inert. Platinum is a particularly useful element of this pair because it has two kinetically inert sets of complexes (divalent and tetravalent) in addition to the complexes of platinum(O), which is a kinetically labile center. The complexes of divalent and tetravalent platinum show significant differences. Divalent platinum forms four-coordinate planar complexes which have a coordinately unsaturated 16-electron d8 platinum center, whereas tetravalent platinum is an 18-electron d6 center which is coordinately saturated in its usual hexacoordination. In terms of mechanistic interpretation one must therefore consider both associative and dissociative substitution pathways, in addition to mechanisms involving electron transfer or inner-sphere atom transfer redox processes. A number of books and articles have been written about replacement reactions in platinum complexes, and a number of these are summarized in Table 13. 

It is apparent from most of the examples previously described that the most common formal oxidation state found for the Group 14 element is E(IV) (E = Ge, Sn, Pb). Relatively few examples of divalent germanium, tin, or lead complexes have been described, and of these, many are not well characterized. Cobalt-containing compounds are no exception in this regard and there appears to be only one report in the literature that describes a species of this type, viz. [Ge Co(CO)4 2], 67, although the precise structure of this complex is unknown (77). Two main synthetic routes are described, Eqs. (4) and (S), the starting complex in the latter reaction being... 

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