9.6     [NiCl_{4}]^{2-}is paramagnetic while [Ni(CO)_{4}] is diamagnetic though both are tetrahedral. Why?

Answers (1)
D Devendra Khairwa

The difference in the magnetic behaviour is due to the nature of ligands present. In case of  [NiCl_{4}]^{2-}  the oxidation state of nickel is +2 and also Cl- is a weak ligand. Thus its configuration becomes:- 


So it is paramagnetic and tetrahedral in nature.

In the case of   [Ni(CO)_{4}] ,  the oxidation state of nickel is 0. So its configuration is 3d8 4s2. We also know that CO is a strong ligand, thus the configuration of nickel becomes:-


Hence the given compound is diamagnetic but tetrahedral in nature.