Preparation of Chloropentaamminecobalt(III) Chloride [Co(NH3)5Cl]Cl2

Introduction The chemistry of the transition metal cobalt (most common oxidation states +2 and +3) is dominated by the stability of the cobalt(II) ion which forms a wide variety of stable complexes with most ligands such as water, ammonia, chloride ion etc. The cobalt(III) state can be stabilised by a suitable ligand and cobalt(III) complexes are usually made by oxidising a cobalt(II) .salt in the presence of the stabilising ligand

- Coordination No. - Coordination geometry.

Experimental Procedure: . 1- In a fume hood, add 5 g of ammonium chloride to 30 mL concentrated aqueous ammonia in a 250-mL Erlenmeyer flask. (The combination of NH4Cl and NH3(aq) guarantees a large excess of the NH3 ligand.). 2- Stir the ammonium chloride solution vigorously using a magnetic stirring plate while adding 10 g finely divided CoCl2⋅6H2O in small portions. 3- Next, add 10 mL 30% hydrogen peroxide to the brown Co slurry, using a buret that has been set up in the hood and filled by the laboratory instructor. An addition rate of about 2 drops per second is usually sufficient, but care should be taken to avoid excessive effervescence in this exothermic reaction. (If the reaction shows signs of excessive effervescence, turning off the magnetic stirrer momentarily will usually prevent overflow of the solution.).

4- When the effervescence has ceased, add 20 mL conc 4- When the effervescence has ceased, add 20 mL conc. HCl with continuous stirring, pouring about 1-2 mL at a time. At this point, the reaction may be removed form the hood. Use a heater to heat the solution to 60°C with occasional stirring. Hold the temperature between 55°C and 65°C for 20 min.; 5- Add 25 mL distilled water, and allow the solution to cool to room temperature. 6- Collect the purple product by filtration through a Buchner funnel; wash it three times with 7.5 mL cold distilled water and twice with 7.5 mL ice-cold ethanol. (The solutions must be cold to prevent undue loss of product by redissolving.).

Experimental Calculations: