Question

What are primary and secondary valency in coordination compounds with examples?

Answer 1

Werner developed the idea of a metal ion having a primary and secondary valency.

Primary valency

• In the coordination complex, primary valencies are ionisable valencies and are equal to the oxidation state of metal ion.
• Primary valencies are non-directional in nature.
  

Examples of primary valency

• Binary compounds, for example ${\mathrm{CrCl}}_3$ ,${\mathrm{PdCl}}_2$ have a primary valency of 3, 2 respectively.
• Another example of primary valency is as follows:-
• In the given complex, the primary valency is 3, as the oxidation number of cobalt$\left(\mathrm{Co}\right)$ is $+3$.

Secondary valency

• The secondary valency is equal to the coordination number of the central metal ion.
• The secondary valencies are directional in nature.
  

Example of secondary valencies

In the given complex, the coordination number of cobalt$\left(\mathrm{Co}\right)$ is 6.