Question

Calculate effective atomic number of \( Fe^{2+} \) in \( [Fe(CN)_6]^{4-} \) [ Given : (Z = 26) ]

Hint:

If the EAN equals 18, 36, 54, or 86, the complex is said to follow the EAN rule, indicating high stability.

Answer 1

Step 1: Understanding the Concept:
The Effective Atomic Number (EAN) represents the total number of electrons surrounding the central metal atom/ion in a complex. Sidgwick proposed that complexes are more stable when the EAN equals the atomic number of the next noble gas.
Step 2: Key Formula or Approach:
\[ \text{EAN} = Z - X + Y \]
Where:
\( Z = \) Atomic number of the metal.
\( X = \) Oxidation state of the metal.
\( Y = \) Electrons donated by ligands (\( 2 \times \text{Coordination Number} \) for monodentate ligands).
Step 3: Detailed Explanation:
1. Find Oxidation State (X):
In \( [Fe(CN)_6]^{4-} \), let oxidation state of Fe be \( a \).
\( a + 6(-1) = -4 \)
\( a - 6 = -4 \Rightarrow a = +2 \). So, \( X = 2 \).
2. Identify Coordination Number (CN):
There are 6 \( CN^- \) ligands. CN = 6.
3. Electrons donated (Y):
\( Y = 2 \times 6 = 12 \).
4. Calculate EAN:
\[ \text{EAN} = 26 - 2 + 12 \]
\[ \text{EAN} = 24 + 12 = 36 \]
Step 4: Final Answer:
The Effective Atomic Number of \( Fe \) in the complex is 36, which corresponds to the noble gas Krypton (\( Kr \)).