Question

Which from following complexes does NOT obey EAN rule?

• A. $[Co(NH_3)_6]^{3+}$
• B. $Cr(CO)_6$
• C. $[Zn(NH_3)_4]^{2+}$
• D. $[Cu(NH_3)_4]^{2+}$

Hint:

EAN rule is obeyed if the result equals the atomic number of the next noble gas ($36, 54,$ or $86$).

Answer 1

The Correct Option is D

Step 1: Formula
$EAN = Z - (\text{Oxidation State}) + 2 \times (\text{Coordination Number})$.

Step 2: Calculation
- (A) $[Co(NH_3)_6]^{3+}$: $27 - 3 + (2 \times 6) = 36$ (Krypton, Obeys) - (B) $Cr(CO)_6$: $24 - 0 + (2 \times 6) = 36$ (Krypton, Obeys) - (C) $[Zn(NH_3)_4]^{2+}$: $30 - 2 + (2 \times 4) = 36$ (Krypton, Obeys) - (D) $[Cu(NH_3)_4]^{2+}$: $29 - 2 + (2 \times 4) = 35$ (Does NOT obey)

Step 3: Conclusion $[Cu(NH_3)_4]^{2+}$ does not reach the noble gas configuration of 36.
Final Answer: (D)