Werner theory of coordination compound

 

Werner theory of coordination compound

·      Proposed by Alfred Werner in 1893

·       He prepared and characterised a large no of coordination compounds and studied their physical and chemical properties

In the series of compounds of cobalt(III) chloride with ammonia, he found that some of the chloride ions could be precipitate as AgCl on adding excess silver nitrate solution in cold but some remained in solution

      1mole   CoCl₃.6NH₃ (yellow) gave à 3mole AgCl

      1mole   CoCl₃.5NH₃ (purple) gave à2mole AgCl

      1mole   CoCl₃.4NH₃ (green₎ gave à1mole AgCl

      1mole   CoCl₃.4NH₃(violet) gave à1mole AgCl

The important postulates of coordination theory are as –

1). in coordination compound, metals show types of valencies/linkage.

      a). Primary valencies

      b). secondary valencies

2). The primary valencies are normally ionisable and satisfied by negative ions.

3). Secondary valencies are non-ionisable and satisfied by neutral molecules or negative    

         Ions. It represents to the coordination number and is fixed for a metal.

4. the ions/group of atoms bound by the secondary linkage to the metal have characteristics spatial arrangement corresponding to different coordination number.

 

In modern formulation –

·      Spatial arrangement of ions/ groups present around to central metal ion is called coordination polyhedral.

·      The species within the square bracket are coordination entities or complex

·      Ions outside the square bracket are called counter ions.

·      Primary valencies usually indicates to the oxidation no. and Secondary valencies refers to the coordination no. of central metal atom/ions.