How would you account for the fact that `[Ni(CO)_4]` has tetrahedral geometry ?

Explanation

The electronic configuration ofNi is `[Ar]3d^8 4s^2 4p^0`. In this complex nickel is in zero oxidation state.

In the fonnation of `[Ni(CO)_4]` complex, when CO molecules approaches Ni atom, they force 4s-electrons to pair up with 3d electrons. The vavant 4s- orbital and three 4p - orbitals hybridise to give four vacant `sp^3`. hybrid orbitals. These four hybrid orbitals are occupied by four pairs of electrons donated by four CO molecules. Hence, the complex `[Ni(CO)_4]` has tetrahedral geometry due to `sp^3` hybridisation. It is dimagnetic in nature due to the absence of unpaired electrons.