Studies of Complexes Containing Ammonia and Other Ligands

7 STUDIES OF COMPLEXES CONTAINING AMMONIA AND OTHER LIGANDS 

Under various experimental conditions, mixed ligand complexes containing ammonia and other ligands, have been prepared. The general method involves the oxidation of a Co(II) salt in presence of ammonia, ammonium chloride and another ligand. Like the other Co(IlI) complexes so far studied, they are low spin, diamagnetic and kinetically inert. They exhibit interesting characteristics. 

Dissolve 5.0 g of cobalt(Il) carbonate in a solution of 15 cm cone. HCI + 35 cm water. Once all gas evolution seems to cease even after warming, filter off any undissolved residue from the technical grade carbonate. Add to the filtrate 5.0 g of ammonium chloride dissolved in 50 cm cone, ammonia in the fume cupboard and then add, slowly and with stirring, 80 cm of 6% hydrogen peroxide. When no more effervescence is observed, draw a stream of air through the solution for an hour. Then add cone. HCI to neutralise the solution (use a dip pH strip) when the complex salt precipitates. Then add 20 cm cone. HCI and heat on a water bath for 2 hours. Wash the precipitate with water by decantation to get rid of any aqua complex and filter at the pump. Wash with small volumes of ethanol and dry by continued suction while pressing between filter paper and eventually heat at 110°C to constant weight. 

1 Conversion to the chloropentaamminecobalt(Ill) chloride Dissolve 5.0 g of your preparation in 50 cm water and add cone. HCl gradually until no more gas is evolved. Add cone, ammonia to neutralise any excess acid (test with pH paper) and add 5 cm of ammonia. Heat, without boiling, for 20 minutes. Cool and add 75 cm cone. HCl and reheat for 30 minutes until the colour changes to purple-red. Cool to room temperature and allow to stand to complete the crystallisation. Wash by decantation with iced water and then filter under suction. Wash on the filter with a little ethanol and suck dry. Complete drying in an oven at 110 C. Weigh as above and compare with the product obtained in the earlier experiment. 

---