Question

Explain on the basis of valence bond theory that [NI(CN)^2-] ion with square planar structure is diamagnetic and the [NI(CN)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. dsp² – hybrid orbitals

CN^- is a strong ligand as it approaches the metal ion, So the electrons should getd paired up.

In [NI(CN)₄]^2- , Cl^- provides a weak ligand field. It is therefore unable to pair up the unpaired electrons of the 3d orbital.

Hence the hybridisation is sp³ , and it is paramagnetic