Question

Explain the structure of tetrachloronickelate(II) [NiCI]^2- on the basis of valence bond theory.

Answer 1

(1) Tetrachloronickelate(II) ion is an anionic complex,

Oxidation state of Ni is +2 and the coordination number is 4.

(2) Electronic configuration : ₂₈Ni [Ar]¹⁸3d⁸ 4s² 4p°

Electronic configuration : Ni²⁺ [Ar]¹⁸ 3d⁸4s°4p°

(3) Since the coordination number is 4, 

It gets 4 vacant hybrid orbitals by sp³ -hybridisation of one 4s and three 4p orbitals giving tetrahedral geometry to the complex.

(4) As Cl is a weak ligand, 

2 unpaired electrons in Ni²⁺ remain undisturbed.

(5) 4 lone pairs of electrons from 40 ligands are accommodated in the vacant four sp hybrid orbitals. 

Thus,

Four sp³ hybrid orbitals of Ni²⁺ overlap with filled orbitals of Cl^- forming 4 coordination bonds, giving tetrahedral geometry to the complex.

Since the complex has 2 unpaired electrons, 

It is paramagnetic.

Magnetic moment μ is,

μ = \(\sqrt{n(n+2)}\)

= \(\sqrt{2(2+2)}\)

= 2.83 B.M.