Question

What magnetic behaviours are expected for [Ni(CO)₄] and [NiCl₄]²⁻ and why?

Answer 1

1. The magnetic behaviours of [Ni(CO)₄] and [NiCl₄]²⁻ differ due to the nature of the ligands and the geometry of the complexes, which influence electron pairing and hybridisation.
2. In [Ni(CO)₄]: 
   • Nickel is in the zero oxidation state (Ni⁰) with an electron configuration of 3d⁸ 4s².
   • The ligand CO is a strong field ligand, which causes pairing of the 3d electrons.
   • As a result, all electrons become paired.
   • The complex undergoes sp³ hybridisation, forming a tetrahedral geometry.
   • Because there are no unpaired electrons, [Ni(CO)₄] is diamagnetic.
3. In [NiCl₄]²⁻: 
   • Nickel is in the +2 oxidation state (Ni²⁺), with an electron configuration of 3d⁸.
   • The Cl⁻ ligand is a weak field ligand, which does not cause the pairing of electrons in the 3d orbitals.
   • The complex also forms a tetrahedral geometry through sp³ hybridisation, but two unpaired electrons remain in the 3d orbitals.
   • The [NiCl₄]²⁻ is paramagnetic due to the presence of unpaired electrons.