Tetracyano nicklate is diamagnetic whereas tetracholoronicklate is paramagnetic why ?

[Ni(CN)₄]^2- = Ni²⁺ + 4CN^-

* In [Ni(CN)₄]^2-, there is Ni²⁺ ion for which the electronic configuration in the valence shell is 3d⁸ 4s⁰.

* In presence of strong field CN^- ions, all the electrons are paired up. The empty 4d, 3s and two 4p orbitals undergo dsp²hybridization to make bonds with CN^- ligands in square planar geometry. Thus [Ni(CN)₄]^2- is diamagnetic

NiCl₄^2- = Ni²⁺ + 4Cl^-

* Again in NiCl₄^2-, there is Ni²⁺ ion, However, in presence of weak field Cl^- ligands, NO pairing of d-electrons occurs. Therefore, Ni²⁺ undergoes sp³ hybridization to make bonds with Cl^- ligands in tetrahedral geometry. As there are unpaired electrons in the d-orbitals, NiCl₄^2- is paramagnetic

Regards

Arun (AskIITians Forum Expert)