`[Ni(CN)_4 ]^(2-) ` is diamagnetic ,while ` [NiCl_4]^(2) - ` is paramagnetic ,explain using crystal field theory.

Explanation

`[Ni(CN)_4 ]^(2-) ` is a low spin square planar complex as it contains strong field ` CN^(-) ` ligand in it Oxidation state of Ni in complex is +2 Electronic Configuration of ` Ni^(2+) is 3d^(8) 4s^(0) `

Crystal field splitting in square planar complex.
No unpaired electrons so the complex is diamagnetic.
` [NiCl_4]^(2-) ` is a high spin tetrahedral complex as it contains weak field ` C1^(-)` ligand in it . Oxidation state of Ni in complex in +2 Electronic Condiguration of ` Ni^(2+) is 3d^(8) 4s^(6) `
` (##SUR_CHE_XII_V01_C05_E02_019_S02.png" width="80%">
It has two unpaired electrons ,so the complex is paramagnetic.