Question

Which of the following co-ordinate complexes if an exception to EAN rule?
(Given atomic number Pt = 78, Fe = 26, Zn = 30, Cu = 29)

Options

• [Pt(NH₃)₆]⁴⁺

• [Fe(CN)₆]^4-

• [Zn(NH₃)₄]²⁺

• [Cu(NH₃)₄]²⁺

Answer 1

[Cu(NH₃)₄]²⁺ 

Explanation:

EAN = Z (atomic number of the metal)-number of electrons lost in the ion formation+ number of electrons gained from the donor atoms of the ligands.

Complex	Oxidation state of metal ion	Atomic no.	Coordination no.	EAN
[Pt(NH3)6]4+	+ 4	76	6	(78 - 4) + (6 × 2) = 86 (Rn)
[Fe(CN)6]4-	+ 2	26	6	(26 - 2) + (6 × 2) = 36 (Kr)
[Zn(NH3)4]2+	+ 2	30	4	(30 - 2) + (4 × 2) = 36 (Kr)
[Cu(NH3)4]2+	+ 2	29	4	(29 - 2) + (4 × 2) = 35 (Br)

[Cu(NH₃)₄]²⁺ is an exception to EAN rule.