Question

The geometry of diamagnetic nickel complex \([ \text{Ni(CN)}_4 ]^{2-}\) is:

• A. Tetrahedral
• B. Octahedral
• C. Square planar
• D. Distorted octahedral

Hint:

Strong field ligands like CN\(^{-}\) induce pairing of electrons, favoring low-spin square planar complexes in \(d^8\) metal ions like Ni\(^{2+}\).

Answer 1

The Correct Option is C

The complex \([ \text{Ni(CN)}_4 ]^{2-}\) contains Ni in +2 oxidation state. Electronic configuration of Ni is: \[ \text{Ni} = [Ar]\,3d^8\,4s^2 \Rightarrow \text{Ni}^{2+} = [Ar]\,3d^8 \] Cyanide (CN\(^-\)) is a strong field ligand and causes pairing of electrons. Hence, the 3d electrons pair up and the complex becomes low-spin and diamagnetic (no unpaired electrons).
In such cases, the hybridization is \( dsp^2 \), which leads to a square planar geometry.
\[ \boxed{\text{Geometry is square planar due to dsp}^2\ \text{hybridization and strong field ligand}} \]