Question

What is the hybridisation and structure of \([\text{Ni(CN)}_4]^{2-}\)?

Hint:

Strong field ligands like CN\(^-\) cause electron pairing and often result in square planar complexes for \(d^8\) metal ions such as Ni(II).

Answer 1

Step 1: Determine the oxidation state of nickel: \[ x + 4(-1) = -2 \quad \Rightarrow \quad x = +2 \] So, nickel is in the \(+2\) oxidation state.
Step 2: Electronic configuration of Ni (\(Z = 28\)): \[ \text{Ni}^{2+}: [\text{Ar}]\,3d^8 \]
Step 3: CN\(^-\) is a strong field ligand, which causes pairing of electrons in the \(3d\) orbitals.
Step 4: After pairing, one \(3d\), one \(4s\), and two \(4p\) orbitals hybridise to form dsp2 hybrid orbitals.
Step 5: \(\text{dsp}^2\) hybridisation leads to a square planar geometry.