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.

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

Answer 1

Nickel in [Ni(CN)₄]²⁻ is in the +2 oxidation state, i.e., nickel is present as Ni²⁺ ion and dsp² hybrid orbitals.

[Ni(CN)4]2−	Ni(28): 4s2 3d8
	Ni2+(28): 4s0 3d8

CN⁻ is a strong field ligand, so it causes the pairing of electrons.

The strong ligand CN⁻ facilitates electron pairing. The complex is diamagnetic because it contains no unpaired electrons.

In [NiCl₄]²⁻, the formation of the above complex can be explained by hybridization. Ni in the above compound is in the +2 oxidation state, i.e., Ni²⁺.

As Cl⁻ is a weak ligand, pairing of electrons does not take place. sp³ hybridisation of orbitals takes place, giving rise to tetrahedral geometry. As there are two unpaired electrons in the complex, it is paramagnetic.

It is paramagnetic due to the presence of unpaired electrons.