Question

`[NiCl_(4)]^(2-)` is paramagnetic while `[Ni(CO)_(4)]` is diamagnetic though both are tetrahedral. Why?

Answer 1

The `Cl^(-)` is a weak field ligand and cannot cause the electron pairing . On the other hand , CO is a strong field ligand and can cause the electron pairing .
That is why , `(NiCl_(4))^(2-)` is paramagnetic while `[Ni(CO)_(4)]` is diamagnetic nature . For details , consult section 10 .