Question
Explain the bonding in coordination compounds in terms of Werner’s postulates.
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Answer
The main postulates of Werner's theory of coordination compounds are as follows:
- Metals possess two types of valencies called
- Primary valency which are ionisable;
- secondary valency which are non- ionisable
- Primary valency is satisfied by the negative ions and it is that which a metal exhibits in the formation of its simple salts.
- Secondary valencies are satisfied by neutral ligand or negative ligand and are those which metal exercises in the formation of its complex ions. Every cation has a fixed number of secondary valencies which are directed in space about central metal ion in certain fixed directions, e.g,, In CoCl3-6NH3, valencies between Co and Cl are primary valencies and valencies between Co and NH3 are secondary. In COCl3-6NH3, six ammonia molecules linked to Co by secondary valencies are directed to six corners of a regular octahedron and thus account for structure of COCl3-6NH3 as follows:
In modern theory, it is now referred as coordination number of central metal atom or ion.
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