Hexaamminecobalt III Chloride

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

Most authorities attribute the discovery of the first metal ammine to Tassaert, a Parisian chemist about whom virtually nothing is known — not even his first name. In his short article12 he is identified only as Citoyen Tassaert — Citizen Tassaert. Some chemists imply or even openly state that Tassaert was the first to prepare hexaamminecobalt(III) chloride, [Co(NH3)6]C13, the parent compound from which all cobalt ammines may be considered to be derived. Yet he merely observed the brownish mahogany color of the solution formed when excess aqueous ammonia is added to a solution of cobalt chloride or cobalt nitrate, and he failed to follow up his accidental discovery. 

Kekule s instability criterion failed completely in the case of many coordination compounds, which were classified as molecular compounds by sheer dint of necessity although they were extremely resistant to heat and chemical reagents. For example, although hexaamminecobalt(III) chloride contains ammonia, it neither evolves this ammonia on mild heating nor does it react with acids to form ammonium salts. Also, addition of a base to its aqueous solution fails to precipitate hydrated cobalt(III) hydroxide. 

Luteocobaltic chloride (modern, [Co(NH3)6]C13, hexaamminecobalt(III) chloride) is a stable yellow-orange compound.55 In solution, all the chlorine is immediately precipitated by silver nitrate. Treatment with hydrochloric acid at 100 °C does not remove any ammonia. Treatment with sulfuric acid does not remove any ammonia, but yields the compound Co2(S04)3T2NH3, i.e. the chlorine atoms are replaced by sulfate groups. Clearly, some sort of very stable metal—ammonia bonding but much less stable metal—chlorine bonding is indicated. 

A solution of hexaamminecobalt(III) chloride (0.43 g., 0.0016 mole) in 70 ml. of 3.4 M HCl is heated to 70° on a hot plate. To this solution iron(III) chloride 6-hydrate (1.4 g., 0.005 mole) in 10 ml. of hot water is added. The resulting solution is heated for a few minutes until orange crystals begin to form. After the mixture has been cooled to room temperature, the crj stals are collected on a Buchner funnel, washed with alcohol and ether, and dried in an evacuated desiccator over potassium hydroxide or sulfuric acid. A typical jdeld is 0.42 g. (first crop, 60%) plus 0.10 g. (second crop, 14%). Anal. Calcd. for [Co(NH3)6]-[FeCb] N, 19.54 H, 4.18 Cl, 49.55. Found N, 19.52 H, 4.13 Cl, 48.42. (The volumetric chloride anabasis is difficult because of the interference of iron with the end point.)... 

The method of Neville and Gorin —allowing glycine to react with hexaamminecobalt(III) chloride in a boiling aqueous potassium hydroxide solution under reflux—favors formation of the fac isomer. 

The coordination number of a metal atom or ion in a complex is the number of donor atoms to which it is coordinated, not necessarily the number of ligands. The coordination sphere includes the metal or metal ion (called the central atom) and its ligands, but no uncoordinated counterions. For example, the coordination sphere of hexaamminecobalt(III) chloride, [Co(NH3)g]Cl3, is the hexaamminecobalt(III) ion, [CofNLIj) ]. These terms are illustrated in Table 25-5. 

Many complexes originating from cobalt ions comply with the regular octahedron structure. If one prepares the yellow crystalline hexaamminecobalt(III) chloride from pink-colored cobalt(II) chloride, one obtains the octahedral structure of a hexaamminecobalt(III) ion it is a building unit of the crystal lattice. If it is dissolved in water, the complex ion remains intact ... 

Boas et al. prepared and separated the meridional isomers of the [Co(ai-02)2] type complexes (oti-a2 represents the dianion of the dipeptide H2 i-a2> where ai is the N-terminal residue). Seven methods were used to prepare bis(dipeptidato)-cobaltate(III) complexes (i) by oxygenation of cobalt(II), (ii) from cobalt(II) carbonate, (iii) from sodium tricarbonatocobaltate(III), (iv) from hexaamminecobalt-(III) chloride, (v) from hexakis(urea)cobalt(III) perchlorate, (vi) from cobalt(III) hydroxide oxide, (vii) from triammine(glycylglycinato)cobalt(III). The methods starting from Co" gave more minor products, Na3[Co(C03)3] 3 H2O gave less, and cobalt(III) hydroxide oxide gave very little of these products. Thus, the method (vi) was prefered. The peptides used were gly-gly, L-ala-gly, gly-L-ala, L-leu-gly, gly-L-leu, L-phe-gly, gly-L-phe, L-ala-L-ala, L-ala-D-ala, L-leu-L-leu. 

But Kekuld s stability criterion, or to be more accurate, instability criterion failed completely in the case of many coordination compounds, especially the metal-ammines, which were classified as molecular compounds by sheer dint of necessity even though they were extremely resistant to heat and chemical reagents. For example, look at Figure 1. Although hexaamminecobalt(III) chloride contains ammonia, it neither evolves this ammonia on mild heating nor does it react with acids to form ammonium salts. Also, despite its cobalt content, addition of a base to its aqueous solution fails to precipitate hydrated cobalt(III) hydroxide. It remained for Alfred Werner to explain successfully the constitution of such compounds, but the time was not yet ripe. Before considering Werner s coordination theory, we must examine one more theory of coordination compounds, perhaps the most successful of the pre-Wemer theories, namely, the Blomstrand-J0rgensen chain theory. 

Some examples of complexes of cobalt(III) prepared by oxidation-reduction reactions have been given earlier, as part of the description of the substitution reactions of the inert compounds formed. However, the preparation of what may be regarded as the parent complex, hexaamminecobalt(III) chloride, was not described. As Werner found, this is made by hydrogen peroxide oxidation of an aqueous solution of cobalt(II) chloride made alkaline with ammonia in the presence of ammonium chloride ... 

The Brdicka reaction (procedure) is the frequently employed electrochemical method for determination of metallothionein in a variety of biological samples [71-77]. The method uses Brdicka s solution. Brdicka s solution consists of an ammonium buffer (ammonium chloride and ammonium) and hexaamminecobalt(III) chloride complex ([Co(NH3)6]Cl3). 

C/5 -diamminedichloroplatinum(II) is the possible substitution for hexaamminecobalt(III) chloride complex in the Brdicka procedure where the buffer system is the same. This system was described using the method of cyclic voltammetry with the following description of the mechanism [79] ... 

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