Werner's Co-ordination Theory

In 1893, Alfred Werner proposed a theory named as Werner's Co-ordination theory, in which he explained the concept of valence in metal complexes.
According to him, there are two types of valences named as primary valence and secondary valence in metal complexes.





1)     [Co(NH3)6]Cl3 :
According to the Werner's theory, in [Co(NH3)6]Cl3 complex, the primary valence are satisfied by the three chloride ions (longer dotted line) while the six secondary valence are satisfied by six NH3 molecules. These NH3 molecules are very tightly bound to the cobalt metal and hence they don't dissociate in solution. The three Chloride ions are far away from the central cobalt metal and hence they are less firmly held by the metal atom. therefore all three Chloride ion dissociate in solution giving [Co(NH3)6]3+ and 3Cl- ions, with total four ions. 


2)     [Co(NH3)5Cl]Cl2 :
According to the Werner's theory, in [Co(NH3)5Cl]Cl2 complex, the primary valence are satisfied by the two chloride ions (longer dotted line) and one Chloride ion must play the double role to satisfying both primary and secondary valence. This is because the fulfillment of secondary valence is essential. So, in the solution, [Co(NH3)5Cl]Cl2 complex gives [Co(NH3)6Cl]2+ and 2Cl- ions, with total three ions.



3)     [Co(NH3)4Cl2]Cl :
According to the Werner's theory, in [Co(NH3)4Cl2]Cl complex, the primary valence are satisfied by the only one chloride ion (longer dotted line) and two Chloride ions must play the double role to satisfying both primary and secondary valence, hence both are tightly bound to the central metal atom. So in the solution, [Co(NH3)5Cl2]Cl complex gives [Co(NH3)6Cl2]+ and Cl- ions, with total two ions.



4)     [Co(NH3)4Cl3] :
According to the Werner's theory, in [Co(NH3)4Cl3] complex, all three Chloride ions are satisfied by both primary and secondary valences. Hence, all three chloride ions are tightly bound to the central metal atom, so it can’t give any chloride ion in solution. It is a non-electrolyte because no ions are produced in solution.



 

Defects of Werner’s theory: -
Ø Werner’s theory explains structures but don’t explain the nature of bonding within the co-ordination sphere.
Ø This theory fails to explain that certain 4 co-ordinated complexes are square planer whereas some others are octahedral.
Ø This theory also fails to explain the magnetic, colour and optical properties shown by coordination compounds.
Ø This theory does not explain the stability of the complex.


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