Determining Complex Geometries: Ni(CO)₄ and [NiCl₄]^2-

To determine the geometries of the complexes $Ni(CO)_4$ and $[NiCl_4]^{2-}$, we need to consider the central metal ion's oxidation state, its electronic configuration, and the nature of the ligands.

Analysis of $Ni(CO)_4$

• Central Metal Ion: Nickel (Ni)
• Ligand: Carbonyl (CO) - a strong field ligand.
• Oxidation State of Ni: 0 (since CO is neutral).
• Electronic Configuration of Ni: [Ar] $3d^8 4s^2$. In oxidation state 0, Ni has $3d^{10}$ configuration after ligand coordination and rearrangement (due to strong field ligand).
• Coordination Number: 4.
• Hybridization: $sp^3$.
• Resulting Geometry: Tetrahedral.

Analysis of $[NiCl_4]^{2-}$

• Central Metal Ion: Nickel (Ni)
• Ligand: Chloride (Cl^-) - a weak field ligand.
• Oxidation State of Ni: +2 (since $4 \times (-1) + x = -2 \implies x = +2$).
• Electronic Configuration of Ni²⁺: [Ar] $3d^8$.
• Coordination Number: 4.
• Hybridization: $sp^3$ (even though it's $d^8$, weak field ligands and coordination number 4 typically lead to $sp^3$ hybridization and tetrahedral geometry for Ni(II)).
• Resulting Geometry: Tetrahedral.

Conclusion

Both $Ni(CO)_4$ and $[NiCl_4]^{2-}$ exhibit tetrahedral geometries.