Question

Which from the following complexes, the central metal ion does NOT obey the EAN rule?
(Atomic number = Pt = 78, Cu = 29, Zn = 30, Fe = 26)

• A. \([ \text{Zn}(\text{NH}_3)_4 ]^{2+}\)
• B. \([ \text{Cu}(\text{NH}_3)_4 ]^{2+}\)
• C. \([ \text{Pt}(\text{NH}_3)_6 ]^{4+}\)
• D. \([ \text{Fe}(\text{CN})_6 ]^{4-}\)

Hint:

EAN rule is used to determine the stability of metal complexes based on the total number of electrons around the central atom.

Answer 1

The Correct Option is B

Step 1: Understanding the EAN rule.
The Effective Atomic Number (EAN) rule states that the total number of electrons around the central metal atom/ion in a complex should be equal to the atomic number of the nearest noble gas.
Step 2: Analyzing the options.
(A) \([ \text{Zn}(\text{NH}_3)_4 ]^{2+\):} This follows the EAN rule, as Zn has 30 electrons and the complex provides 30 electrons around the metal.
(B) \([ \text{Cu}(\text{NH}_3)_4 ]^{2+\):} This does not follow the EAN rule as copper in this complex would not achieve a noble gas configuration (only 18 electrons).
(C) \([ \text{Pt}(\text{NH}_3)_6 ]^{4+\):} This follows the EAN rule with platinum achieving 36 electrons.
(D) \([ \text{Fe}(\text{CN})_6 ]^{4-\):} This follows the EAN rule as well.
Step 3: Conclusion.
The correct answer is (B) \([ \text{Cu}(\text{NH}_3)_4 ]^{2+\)}.