Question

Using valence bond theory, explain the hybridisation and magnetic character of the following:

[Co(NH₃)₆]³⁺

Answer 1

When ammonia acts as a ligand, it causes the electrons in the 3d orbitals to pair, freeing two 3d orbitals for hybridisation. As a result, the hybridisation is of the d²sp³ type.

Orbitals of Co:

↑ ↓	↑ ↓	↑	↑	↑		↑ ↓
3d						4s		4p

d²sp³ hybridised orbitals of Co:

↑ ↓	↑ ↓	↑ ↓
	3d					d2sp3 hybridisation

[Co(NH₃)₆]³⁺ (low spin complex):  

↑ ↓	↑ ↓	↑ ↓		XX	XX	XX	XX	XX	XX
	3d					d2sp3 hybrid

Since all the electrons in the 3d orbitals are paired after the interaction with NH₃ ligands, there are no unpaired electrons in the complex.

Therefore,  [Co(NH₃)₆]³⁺ complex is diamagneticin nature.