Chelates and the chelate effect
Coordination Compounds · Chemistry
Study notes
[Ni(en)₃]²⁺ (K ≈ 10¹⁸) is far more stable than [Ni(NH₃)₆]²⁺ (K ≈ 10⁸). Explain. Step 1: Both have 6 N donors; enthalpy of Ni–N bonds similar. Step 2: Forming [Ni(en)₃]²⁺: 1 Ni²⁺ + 3 en → complex + 6 H₂O freed... (net +3 particles). Step 3: Forming [Ni(NH₃)₆]²⁺: 1 + 6 → 1 (net −6 particles). Step 4: Entropy hugely favours chelation: ΔS positive → K 10¹⁰× larger!