Hexaamminecobalt II chloride

The ammines of cobalt(II) are much less stable than those of cobalt(III) thermal decomposition of [Co(NH3)6]Cl2 is characterized by reversible loss of ammonia, whereas that of [Co(NH3)6]Cl3 is not. In his classic dichotomy of complexes, Biltz regarded [Co (NH 3)3] Cl 2 as the prototype of the normal complex and [Co(NH3)6]Cl3 as that of the Werner or penetration complex. Hexaamminecobalt-(II) chloride has been prepared by the action of gaseous ammonia on anhydrous cobalt (II) chloride or by displacing water from cobalt(II) chloride 6-hydrate with gaseous ammonia. It may also be synthesized in nonaqueous solvents by passing dry ammonia through solutions of cobalt(II) chloride in ethanol, acetone, or methyl acetate. Syntheses in the presence of water include heating cobalt(II) chloride 6-hydrate in a sealed tube with aqueous ammonia and alcohol and the treatment of aqueous cobalt(II) chloride with aqueous ammonia followed by precipitation of the product with ethanol. The latter method is used in this synthesis. Inasmuch as the compound is readily oxidized by air, especially when wet, the synthesis should be performed in an inert atmosphere. 

Caution. Inasmuch as all operations are to he performed in an inert-atmosphere box, all necessary solutions and apparatus should he placed in the box before starting the preparation. 

The air-free ammonia-saturated absolute ethanol solution used for washing the product is prepared by refluxing the ethanol solution for approximately 30 minutes and then cooling in the absence of air A current of dry ammonia is passed through the ethanol solution during this cooling step (hood ). 

Fifteen grams (0.063 mol) of cobalt (II) chloride 6-hydrate is dissolved, with heating, in 15 ml. of water contained in a 150-ml. flask, and the pink solution is boiled for several minutes to expel all air. The flask is quickly stoppered and placed in the inert-atmosphere box. Air is displaced from the box by maintaining a rapid flow of oxygen-free nitrogen through the box for about one hour, with occasional collapse of the gloves. 

Bbbsch Sitzher. Ahad. Wien, 66, 724 (1867) J. Prakt. Chem., 1J, 

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Twenty-five grams (0.47 mol) of ammonium chloride is dissolved in 150 ml. (about 2.2 mols) of concentrated (14.7 M) aqueous ammonia in a 1-1. Erlenmeyer flask. The solution is continuously agitated while 50 g. (0.21 mol) of finely powdered cobalt (II) chloride 6-hydrate is added in small portions, each portion being dissolved before the next is added. A yellow-pink precipitate of hexaamminecobalt(II) chloride forms with the evolution of heat. 

The black crystalline compound [Co(NH3)8(NO)]Cl2 can be prepared in pure form by saturating an ammoniacal solution of cobalt(II) chloride with nitrogen(II) oxide. Previously reported methods of preparation " result in a product contaminated with hexaamminecobalt(II) chloride, which is only slightly soluble in the solutions used and precipitates together with the black chloride. It should be noted that analysis for cobalt, chlorine, or nitrogen cannot reveal the presence of as much as 10% [Co(NH3)6]Cl2 in a sample of (Co(NH3)b(NO)]C12. The best tests for purity are microscopic examination or magnetic measurements. ... 

In order to avoid this contamination, the procedure described herein utilizes a somewhat higher temperature and a lower concentration of ammonia than has previously been suggested. " The formation of the pink precipitate of hexaamminecobalt(II) chloride is thereby completely eliminated. An additional advantage of the procedure is that no special apparatus is required. - - ... 

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. 

Bis(2,4-pentanedionato)diaquocobalt(II) was first obtained b Gach by warming 2,4-pentanedione (acetylacetone) with precipitated cobalt(II) hydroxide. Jones prepared the compound by adding 2,4-pentanedione to an aqueous solution of hexaamminecobalt(II) ion. Recent workers have employed the method of Charles and Pawlikowski, which consists of adding sodium acetate solution to a water-methanol solution of cobalt(II) chloride and 2,4-pentanedione, followed by recrys-tallization from methanol. Bullen grew crystals from dimethyl-formamide for an x-ray diffraction study. 

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. 

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 ... 

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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