Question

Explain the formation of [Co(NH₃)₆]³⁺ ion on the basis of Valence bond theory.

Answer 1

1. The oxidation state of Cobalt is +3
2. The valence shell electronic configuration of Co³⁺ is represented in the box diagram as shown below:
   

   3d						4s		4p
   ↑↓	↑	↑	↑	↑

3. The number of ammine ligands is 6, and the number of vacant metal ion orbitals required for bonding with ligands must be six.
4. Complex is low spin, so pairing of electrons will take place prior to hybridisation.
5. Electronic configuration after pairing would be 
   

   3d						4s		4p
   ↑↓	↑↓	↑↓

6. Six orbitals available for hybridisation are two 3d, one 4s, three 4p orbitals
   
   The orbitals for hybridization are decided from the number of ammine ligands, which is six. Here (n − 1)d orbitals participate in hybridization since it is the low spin complex.
7. Electronic configuration after complex formation.
   
   
8. As all electrons are paired, the complex is diamagnetic.