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

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.

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