Coordination Compounds : Werner theory

Werner was able to explain the bonding in complex.

Primary valency (Pv) : This is non- directional and ionizable. In fact it is the positive charge on the metal ion.

Secondary valency (Sv) : This is directional and non- ionizable. It is equal to the number of ligand atoms co-ordinated to the metal (co-ordination number).

 

Example : [Co(NH3)6]Cl3 or Co(NH3)6]3+3Cl
Pv → 3Cl[3] Sv → 6NH3(6)
[Co(NH3)5Cl]Cl2

Pv → 2Cl(2)

or

Sv

[Co(NH3)5Cl2+2Cl

→5NH3 + 1Cl (6)

[Co(NH3)4Cl2Cl or [Co(NH3)4Cl2]+Cl
Pv → Cl(1) Sv →4NH3 + 2Cl(6)

         

Nature of the complex can be understood by treating the above complexes with excess of AgNO3.

          CoCl3. 6NH3 → 3AgCl, [Co(NH3)6Cl3 (three chloride ion)

          CoCl3. 5NH3 → 2AgCl, [Co(NH3)5Cl2 (two chloride ion)

          CoCl3. 4NH3 → 1AgCl, [Co(NH3)4Cl2 (one chloride ion)

          CoCl3. 3NH3 → no AgCl, [Co(NH3)3Cl3 (no chloride ion)

The nature of bonding between central metal atom and ligands in the coordination sphere has been explained by the three well-known theories. These are :