How does valence bond theory account for: `[Ni (Cl_4)]^(2-)` is diamagnetic and tetrahedral (At number of Ni = 28)

Explanation

In `[NiCl_4]^(2-)]` O.S. of nickelis +2. `Ni^(2+)` is a `d^8` ion. Due to the presence of weak ligands `(Cl^(-))` in `[NiCl_4]^(2-)`, the two unpaired electrons in nickel ion `(Ni^(2+))` do not pair up. Here `Ni^(2+)` ion undergoes `sp^3`-hybridisation to accomodate the four pairs of electrons from four chloride ions `(Cl^(-))`. As the complex contains two unpaired electrons, it is paramagnetic. The shape of the complex is tetrahedral due to the `sp^3` hybridisation of `Ni^(2+)` ion.