Coordination Compounds

Question
CBSEENCH12007306

Explain on the basis of valence bond theory that [Ni(CN)4]2–  ion with square planar is diamagnetic and the [NiCl4]2– ion with tetrahedral geometry is paramagnetic.

Solution

(i) [Ni(CN)4]2–


Ni is in the +2 oxidation state i.e., in d8 configuration.
There are 4 CN− ions. Thus, it can either have a tetrahedral geometry or square planar geometry. Since CN− ion is a strong field ligand, it causes the pairing of unpaired 3d electrons.






CN will cause pairing of electrons. It is diamagnetic in nature due to the unpaired electron. 


(ii) [Ni(Cl
4)]2–

In case of [NiCl4] 2−, Cl ion is a weak field ligand. Therefore, it does not lead to the pairing of unpaired 3d electrons. Therefore, it undergoes sp3 hybridization. Since there are 2 unpaired electrons in this case, it is paramagnetic in nature.



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