Objectives Coordination Compounds are the backbone of modern inorganic and bio–inorganic chemistry and chemical industry. Alfred Werner ( - ), a Swiss chemist was the first to formulate his ideas about the structures of coordination compounds. He prepared and characterised a large number of coordination compounds and studied their physical and chemical behaviour by simple experimental techniques. Werner proposed the concept of a primary valence and a secondary valence for a metal ion.
Binary compounds such as CrCl , CoCl or PdCl have primary valence of , and respectively. In a series of compounds of cobalt(III) chloride with ammonia, it was found that some of the chloride ions could be precipitated as AgCl on adding excess silver nitrate solution in cold but some remained in solution.