What is the geometry of [Ni(CO)]-4?
The correct answer and explanation is :
The geometry of the complex ion $[Ni(CO)_4]^{-}$ is tetrahedral.
Explanation:
To understand why $[Ni(CO)_4]^{-}$ adopts a tetrahedral geometry, we need to examine its electronic structure, bonding, and the characteristics of the involved ligands.
- Oxidation State of Nickel: In the complex $[Ni(CO)_4]^{-}$, the carbon monoxide (CO) ligands are neutral, and the overall charge of the complex is $-1$. The oxidation state of nickel (Ni) in this case is $+1$, as the sum of the charges of the ligands (each CO being neutral) and the complex ion’s overall charge must add up to $-1$.
- Electron Configuration of Ni$^+$: Nickel has an atomic number of 28, so its neutral atomic configuration is [Ar] 3d$^8$ 4s$^2$. In the +1 oxidation state, Ni$^+$ loses one electron, resulting in the configuration [Ar] 3d$^8$. This gives the Ni$^+$ ion 8 valence electrons available for bonding.
- Ligand Donation and Bonding: Each CO molecule is a strong ligand, donating a lone pair of electrons to form a coordinate bond with the metal center. CO acts as a $\sigma$-donor and can also interact with the metal through its $\pi$-electrons. In total, four CO molecules coordinate to the Ni$^+$ ion, contributing their lone pairs of electrons for bonding.
- Tetrahedral Geometry: Given that Ni$^+$ has 8 valence electrons and is bonded to four identical CO ligands, the complex adopts a geometry that minimizes electron pair repulsion, which is tetrahedral in this case. The tetrahedral arrangement allows for the optimal distribution of electron density around the central metal ion.
- Ligand Field Theory: According to ligand field theory, the Ni$^+$ ion in $[Ni(CO)_4]^{-}$ experiences a symmetrical ligand field from the four CO ligands. This results in a tetrahedral structure because the four ligands are evenly spaced, providing the most stable arrangement for the 4 bonding pairs of electrons.
Thus, the geometry of $[Ni(CO)_4]^{-}$ is tetrahedral due to the nature of the bonding and the spatial arrangement of the ligands around the nickel center.