Question

Describe the magnetic behaviour of [Ni(CO)₄].

Answer 1

The complex [Ni(CO)₄] exhibits diamagnetic behaviour, and this can be explained using valence bond theory.

• Nickel (Ni) has atomic number 28, so its ground-state configuration is:
  Ni: [Ar] 3d₈ 4s²
• In [Ni(CO)₄], nickel is in the zero oxidation state (Ni⁰), so it retains the above configuration: 3d⁸ 4s²
• The ligand CO is a strong field ligand and causes pairing of electrons in the 3d orbitals.
• As a result of pairing, all 3d electrons become paired, and the 4s and 4p orbitals are used to form sp³ hybrid orbitals.
• These sp³ hybrid orbitals accept electron pairs from the four CO ligands, resulting in a tetrahedral geometry.
• Since all electrons are paired, [Ni(CO)₄] is diamagnetic (it is not attracted to a magnetic field).