Synthesis of Chloropentaamminecobalt(iii) chloride

Synthesis of Chloropentaamminecobalt(iii) chloride; Characterization and study of its Application

1. Synthesis of Chloropentaamminecobalt(iii) chloride;
Characterization and study of its Application
Abstract:
Chloropentaamminecobalt(III) chloride, probably the oldest known
coordination complex, has been prepared by a large variety of methods.
Those employing previously formed cobalt(III) complexes include
heating [Co(NH 3)5(H20)](NO3)3, [Co(NH 3)5(CO3)]NO3, or
[Co(NH3)5(NO2)] (NO3)2 with concentrated hydrochloric acid.
Treatment of [Co(NH 3)4(H20)2](NO3)3, [Co(NH3)4Cl2]NO3, or
[Co(NH3)4(H20)Cl](N03)2, as well as [Co(NH3)3(H20)Cl2]NO3, with
excess aqueous ammonia followed by hot hydrochloric acid also produces
the desired salt.
Introduction:
Chloropentamminecobalt(iii) chloride is the dichloride salt of the
coordination complex [Co(NH3)5Cl]2+. It is a red-violet, diamagnetic,
water-soluble salt. The compound has been of academic and historical
interest.
The cobalt 2+ ion is more stable than the cobalt 3+ ion for simple salts of
cobalt. Only a few salts of Co(ii) such as CoF3 are known. However,
complexation stabilizes the higher oxidation state, and a number of very
stable octahedrally coordinated complexes of cobalt(III) are known.
The equations of the preparation of [Co(NH3)5Cl]Cl2 are written :
Co
2+
+ NH
4
+
+ 1/2H
2
0
2
→ [Co(NH
3
)
5
H
2
0]
3+

[Co(NH
3
)
5
H
2
0]
3+
+ 3Cl
-
→ [Co(NH
3
)
5
Cl]Cl
2
+ H
2
0

2. Experimental Study:
A rapid and simpler synthesis, which utilizes the reaction of hydrogen
peroxide with ammoniacal cobalt(II) chloride in the presence of
ammonium chloride, is:
Twenty-five grams (0.47 mol) of ammonium chloride is dissolved in
150ml. (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.
All subsequent operations must be perf armed in a hood. To the warm
slurry, 40 ml. (0.39 mol) of 30% hydrogenperoxide is added, with good
swirling or mechanical stirring of the solution, in a thin stream from a
buret. This results in a vigorous exothermic reaction with effervescence.
When the effervescence has virtually ceased, a deep-red solution of the
aquopentaammine salt has formed. To this, 150 ml (1.8 mols) of
concentrated hydrochloric acid (12 M) is added slowly. During the
neutralization, the temperature of the reaction mixture rises, and the
purple product precipitates, leaving a pale blue-green supernatant liquid.
The mixture is heated for 15 minutes on a steam bath, cooled to room
temperature, and filtered by suction. The precipitated product is washed
with several portions of ice cold water totaling 100 ml, followed by an
equal volume of cold 6 M hydrochloric acid. An alcohol wash followed
by an acetone wash facilitates drying, which is accomplished by heating
the product at 100° to 110° for 1 to 2 hours. The yield is 48 to 50 grams
(91 to 95%).
The product is pure enough for further synthetic work but may be
recrystallized as follows with about 95% recovery. The solid is dissolved
in 450 ml. of 1 M aqueous ammonia by warming gently on the steam bath,

3. after which the clear solution is poured (hood!) into 450 ml of
concentrated (12 M) hydrochloric acid. After heating for 45 minutes on a
steam bath, the complex salt is isolated as above.
Result:
Three to four milliequivalents (0.75 to 1.0g) of the compound is dissolved
in 25 ml of hot water containing 5ml of 6N aqueous sodium hydroxide.
The mixture is digested near the boiling temperature for at least 15
minutes and filtered through a very close-textured paper. The residual
cobalt(III) oxide is washed thoroughly on the paper with hot distilled
water until free of chloride, as indicated by testing the filtrate with silver
nitrate. The filtrate and washings are reserved for chloride analysis.
Cobalt is determined iodometrically. The filtrate is just neutralized to
phenolphthalein with dilute nitric acid, and chloride is determined by the
Mohr method. Anal. Calcd. For [Co(NH3)5Cl]Cl2: Co, 23.5; Cl, 42.5.
Found: Co, 22.9; Cl, 42.4.
Characterization:
Chloropentaamminecobalt(III) chloride forms red-violet rhomb-shaped
crystals with Formula Weight: 250.44, Density: 1.819, Odor: Odorless
which decompose on heating above 150° with the stepwise loss of
ammonia. The solubility of the salt in water at 25 ° is 0.4 g./100 ml. The
compound readily aquates in hot water, forming the aquopentaammine
chloride. Chloropentaamminecobalt(III) chloride reacts with hot aqueous
ethylenediamine or dl -propylenediamine to form
tris(ethylenediamine)cobalt(III) chloride or the corresponding
propylenediamine compound, with liberation of ammonia. Concentrated
sulfuric acid at room temperature produces a complex hydrogen sulfate of
the chloropentaamminecobalt(III) ion. Aqueous mercury(II) chloride
forms a characteristic precipitate of a double salt, [Co(NHa)
5Cl]Clz·3HgC12, suitable for microchemical identification.

4. Application:
A nanocomposite of nanophotoadduct of pentaamminechlorocobalt(III)
chloride with hexamine and polythiophene (PTh)may be used in high
temperatures electrical appliances. It may be used along with potassium
tris(oxalato)chromate(III) to synthesize heterometallic compound,
[CoCl(NH3)5][KCr(C2O4)3]•0.5H2O.This heterometallic compound has
several potential applications such as microporous hybrid material with
organic & donors.
References:
1. F. BASOLO and R. K. MURMANN: INORGANIC SYNTHESES,
4, 171 (1953).
2. G. SCHLESSINGER: ibid., 6, 175 (1960).
3. G. SCHLESSINGER: ibid., 6, 182 (1960).
4. W. BILTZ: "Laboratory Methods of Inorganic Chemistry," 2d ed., p.
173, John Wiley & Sons, Inc., New York, 1928.
5. H. H. WILLARD and D. HALL: J. Am. Chem. Soc., 44, 2220 (1922);
H. DIEHL, H. CLARK, and H. H. WILLARD: INORGANIC
SYNTHESES, 1, 186 (1939).
6. W. PALMER: "Experimental Inorganic Chemistry," p. 540,
Cambridge University Press, New York, 1954.
7. L. GMELIN: "Handbuch der anorganischen Chemie," Vol. 58B, p.
151, Verlag Chemie, Berlin, 1930.