Which of the following complex ions violates Sidgwick's Effective Atomic Number (EAN) rule by failin — Coordination Compounds Chemistry Question

💡 Solution & Explanation

EAN is calculated as $Z - \text{O.S.} + 2(\text{C.N.})$. (A) $[Pt(NH_3)_6]^{4+}$: Pt(78) in +4. $EAN = 78 - 4 + 12 = 86$ (Rn). Obeys. (B) $[Fe(CO)_5]$: Fe(26) in 0. $EAN = 26 - 0 + 10 = 36$ (Kr). Obeys. (C) $[Fe(CN)_6]^{4-}$: Fe(26) in +2. $EAN = 26 - 2 + 12 = 36$ (Kr). Obeys. (D) $[Mn(H_2O)_6]^{2+}$: Mn(25) in +2. $EAN = 25 - 2 + 12 = 35$. Fails to attain 36 (Kr).