question_answer 6)

 [NiCl4]2– is paramagnetic while [Ni(CO)4] is diamagnetic though both are tetrahedral. Why?

Answer:

In [Ni(CO)4], Ni is in zero oxidation state. In the presence of ligand CO, the 4s electrons shift to 3d to pair up 3d-electrons. Thus, no unpaired electron is present and hence it is diamagnetic. In (NiCl4)2–, Ni is in +2 oxidation state. Cl– being a weak ligand is unable to pair up the unpaired electrons. Thus, this complex has two unpaired electrons and is paramagnetic.