Synthesis and Characterization of [Co(NH3)5Cl]Cl2
May be extended with the synthesis of [Co(NH3)5ONO]Cl2 and [Co(NH3)5NO2]Cl2.
The aim of this exercise is to prepare [Co(NH3)5Cl]Cl2 from CoCl2∙6H2O, to be measured with Powder
X-Ray Diffraction at Dept. of Chemistry (Aarhus University) as part of SRP Project 01.
The prepared [Co(NH3)5Cl]Cl2 may further be used as starting material the preparation of the two
isomeric complexes [Co(HN3)5ONO]Cl2 and [Co(NH3)5NO2]Cl2. These two complexes represent an
example of linkage isomeri. They are not suited for inclusion in the Powder X-Ray Diffraction
measurements, however.
Chloropentaaminecobalt(III) chloride [Co(NH3)5Cl]Cl2.
2CoCl2∙6H2O + 8NH3 + 2NH4Cl + H2O2 → 2[Co(NH3)5Cl]Cl2 + 14H2O
A solution of 5 g cobalt(II)chloride hexahydrate in 5 mL water is mixed with a solution of 10 g
ammonium chloride in 30 mL concentrated ammonia solution and 5 mL water in a 100 mL conical
flask.
2 mL 30% hydrogen peroxide is added, and the flask is shaken for ca. 3 min. This procedure is repeated
three times and the reaction mixture is then poured into a 250 mL beaker and left at room temperature
for ca. 15 min. with frequent stirring. From a separatory funnel 35 mL concentrated hydrochloric acid
is added carefully while stirring is continued. The mixture is then heated during stirring to the boiling
point for ca. 3 min. (beware of bumping).
The solution is left to cool to room temperature. The purple red crystals are filtered on a glass filter
funnel. They are washed, first with ca. 15 mL 4 M hydrochloric acid (to remove the ammonium
chloride), then with ca. 10 mL 96% ethanol (to remove the hydrochloric acid). The product is dried at
room temperature. The amount of product is ca. 5 g, corresponding to a yield of 97%.
Characterization
The crystal phase contents and purity of [Co(NH3)5Cl]Cl2 is measured by X-ray powder diffraction. If
time allows, the number of free and coordinated Cl- ions in [Co(NH3)5Cl]Cl2 can be determined by
potentiometric titration with AgNO3.
Addendum:
Nitropentaaminecobalt(III) chloride [Co(NH3)5NO2]Cl2
[Co(NH3)5Cl]Cl2 + NaNO2
H+
→ [Co(NH3)5NO2]Cl2 + NaCl
2.5 g chloropentaaminecobalt(III) chloride is dissolved by heating in a mixture of 25 mL water and 3
mL concentrated ammonia solution in a 100 mL conical flask. After filtering (only if the whole product
has not been dissolved) the solution is made acidic with diluted hydrochloric acid and thereafter 3.0 g
sodium nitrite is added. The reaction mixture is heated on a water bath until the red precipitate has
disappeared. After cooling of the yellow-brown solution, 35 mL concentrated hydrochloric acid is
carefully added under shaking.
After careful cooling, the product is filtered on a glass filter funnel, washed with cold 6 M hydrochloric
acid and then with ca. 10 mL 96% ethanol. The product (yellowbrown crystals) is dried in air at room
temperature. The yield is ca. 2 g, corresponding to 77%.
Nitritopentaaminecobalt(III) chloride, [Co(NH3)5ONO]Cl2
[Co(NH3)5Cl]Cl2 + NaNO2 → [Co(NH3)5ONO]Cl2 + NaCl
2.5 g chloropentaaminecobalt(III) chloride is dissolved by heating in a mixture of 40 mL water and 3
mL concentrated ammonia solution in a 100 mL conical flask. After cooling the mixture is filtered
(only if the whole product has not been dissolved), and the mixture is neutralized precisely with diluted
hydrochloric acid. During heavy shaking 3.0 g sodium nitrite is added, and when the nitrite is dissolved
2.5 mL 6 M hydrochloric acid is added drop wise. A red sediment, consisting mainly of
[Co(NH3)5Cl]Cl2, is immediately precipitated. After cooling under water for ca. one hour the impurities
are dissolved and transformed, and a clean product of crimson coloured crystals can be isolated by
filtering on a glass filter.
The precipitate is washed, first with ca. 5 mL cold water, then with a ca. 10 mL 96% ethanol, and it is
dried in air at room temperature. End product ca. 2 g corresponding to
77%.