Question

The EAN (Effective Atomic Number) of Iron in \([Fe(CN)_6]^{4-}\) is:

• A. 34
• B. 35
• C. 36
• D. 38

Hint:

A complex whose EAN equals the atomic number of the next noble gas (like 36 for Krypton) is generally considered very stable.
This is known as following the EAN rule.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The Effective Atomic Number (EAN) rule was proposed by Sidgwick to explain the stability of coordination complexes.
It represents the total number of electrons present around the central metal ion after coordination.

Step 2: Key Formula or Approach:
The EAN is calculated using the established formula: \( \text{EAN} = Z - \text{O.S.} + 2 \times (\text{C.N.}) \).
Here, \( Z \) is the atomic number of the central metal, \( \text{O.S.} \) is its oxidation state, and \( \text{C.N.} \) is the coordination number.

Step 3: Detailed Explanation:
Let's analyze the given complex ion, \( [\text{Fe(CN)}_6]^{4-} \).
The central metal atom is Iron (\( \text{Fe} \)), which has an atomic number of \( Z = 26 \).
Next, we calculate the oxidation state (\( \text{O.S.} \)) of Iron, let's call it \( x \).
The cyanide ligand (\( \text{CN}^- \)) is a unidentate ligand with a charge of \( -1 \).
The sum of the charges of the metal and ligands equals the overall charge of the complex.
\[ x + 6(-1) = -4 \]
\[ x - 6 = -4 \]
\[ x = +2 \]
Thus, the oxidation state of Iron is \( 2 \).
The coordination number (\( \text{C.N.} \)) is the total number of coordinate bonds formed, which is \( 6 \) since there are six \( \text{CN}^- \) ligands.
Now, we substitute these values into the EAN formula:
\[ \text{EAN} = 26 - 2 + 2 \times 6 \]
\[ \text{EAN} = 24 + 12 \]
\[ \text{EAN} = 36 \]

Step 4: Final Answer:
The EAN of Iron in the given complex is 36.