Question

In potassium ferrocyanide, there are ____ pairs of electrons in the \(t_{2g}\) set of orbitals.

Hint:

Strong field ligands like CN⁻ cause maximum pairing of electrons in the lower energy t₂g orbitals, resulting in low-spin configurations in octahedral complexes.

Answer 1

Correct Answer: 3

Step 1: Electronic Configuration of Fe²⁺ 

• The complex is K₄[Fe(CN)₆].
• In this complex, Fe is in the +2 oxidation state:

Step 2: Effect of Strong Field Ligand (CN⁻)

• CN⁻ is a strong field ligand as per the spectrochemical series.
• It causes pairing of electrons in the d-orbitals.
• The t_2g set of orbitals (lower energy) gets fully filled with 6 electrons, forming 3 pairs.

Step 3: Diagrammatic Representation

The electronic configuration in the d-orbitals is:

\[ t_{2g}^6 e_g^0 \]

The t_2g set contains 6 electrons, forming 3 electron pairs.

Final Answer:

The number of electron pairs in the t_2g set is: 3.