Question

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

Answer 1

Explanation:

CN is strong field legend it causes pairing

while Cl is weak field legend hence it does not cause pairing of electrons

Answer 2

Explanation:

Ni is in the state of+ 2 oxidation, i.e. the configuration of d8.  There are four CN ions. It can therefore have either a tetrahedral geometry or a square planar geometry. Because CN-ion is a powerful field ligand, unpaired 3d electrons are paired. It is now being hybridized by dsp2. It's diamagnetic since all electrons are paired.

Cl-ion is a fragile field ligand for [ Ni(CN)4]2-.Hence, it does not lead to unpaired 3d electrons being paired. Therefore, it is hybridized by sp3. Because in this situation there are 2 unpaired electrons, it is paramagnetic in nature