Question

Discuss the formation of [Ni(CO)₄] on the basis of valence bond theory.

Answer 1

1. Nickel in [Ni(CO)₄] has oxidation state zero.
2. The atomic number of Ni is 28, and its ground state electronic configuration is [Ar] 3d⁸ 4s².
3. In the presence of strong field ligands like CO, the unpaired electrons in the 3d orbitals get paired up due to the strong ligand field effect.
4. As a result, the 3d orbitals become completely filled (3d¹⁰), while the 4s orbital becomes empty.
5. The vacant 4s and three 4p orbitals undergo sp³ hybridisation, forming four equivalent hybrid orbitals arranged tetrahedrally.
6. Each CO ligand donates a lone pair of electrons into these sp³ hybrid orbitals, forming four coordinate covalent bonds.

Hence, according to VBT, [Ni(CO)₄] is a tetrahedral and diamagnetic complex, since all the electrons are paired after rearrangement.