Question

The hybridization and geometry of $([\text{Ni}(\text{CN})_4]^{2-})$ are respectively:

• A. $\text{sp}^3$, tetrahedral
• B. $\text{dsp}^2$, square planar
• C. $\text{d}^2\text{sp}^3$, octahedral
• D. $\text{sp}^2$, trigonal planar

Hint:

For four-coordinate Nickel complexes:
If the ligand is a weak field (like \(\text{Cl}^-\)), no pairing occurs, leading to \(sp^3\) hybridization and tetrahedral geometry.
If the ligand is a strong field (like \(\text{CN}^-\)), pairing occurs, leading to \(dsp^2\) hybridization and square planar geometry.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The objective is to determine the hybridization and molecular geometry of the tetracyanidonickelate(II) complex ion, \([\text{Ni}(\text{CN})_4]^{2-}\).

Step 2: Key Formula or Approach:
We determine the oxidation state of the metal, identify its electronic configuration, analyze the field strength of the ligand, and determine the configuration and hybridization of the orbitals.

Step 3: Detailed Explanation:

• Oxidation State of Nickel:
  In \([\text{Ni}(\text{CN})_4]^{2-}\), let the oxidation state of Nickel be \(x\).
  \[ x + 4(-1) = -2 \implies x = +2 \]
  
• Electronic Configuration: The configuration of neutral \(\text{Ni}\) is \([Ar] 3d^8 4s^2\). For \(\text{Ni}^{2+}\), it is \([Ar] 3d^8 4s^0\).
  
• Ligand Field Strength: Cyanide (\(\text{CN}^-\)) is a very strong-field ligand according to the spectrochemical series.
  
• Electron Pairing: The strong-field ligand forces the pairing of the two unpaired electrons in the \(3d\) orbitals of \(\text{Ni}^{2+}\).
  
• Available Orbitals: Pairing leaves one of the \(3d\) orbitals empty. The empty orbitals available for bonding are: one \(3d\), one \(4s\), and two \(4p\) orbitals.
  
• Hybridization and Geometry: These four orbitals hybridize to form four equivalent \(dsp^2\) hybrid orbitals. A \(dsp^2\) hybridized complex adopts a square planar geometry.
  
• Magnetic Properties: Since all the electrons are paired up after pairing, the complex is diamagnetic.
  

Step 4: Final Answer:
The hybridization is \(dsp^2\) and the geometry is square planar, which corresponds to option (B).