JEE Main 2022 · 25 July · evening · Single correct · +4 / −1
The correct order of energy of absorption for the following metal complexes is :
A : [Ni(en)₃]²⁺ , B : [Ni(NH₃)₆]²⁺ , C : [Ni(H₂O)₆]²⁺
- (a) C < B < A
- (b) B < C < A
- (c) C < A < B
- (d) A < C < B
Answer and solution
Answer (a) C < B < A
Solution
Chemistry ma’am · 4 steps
Same metal ion, same charge, so only the ligand sets the splitting. Rank the ligands.
- What is fixed. All three are octahedral complexes of Ni²⁺, a d⁸ ion. The metal and its oxidation state are the same, so only the ligand field strength changes the size of Δₒ.
- Energy absorbed. The colour comes from a d–d transition, so the energy absorbed grows with Δₒ. A stronger-field ligand gives a larger Δₒ and absorbs light of higher energy, that is, shorter wavelength.
- Spectrochemical series. The series runs H₂O < NH₃ < en. Ethylenediamine binds through two N atoms and forms a chelate ring, so it splits the d orbitals more than NH₃ does.
Complex Ligand Field strength Energy absorbed C: [Ni(H₂O)₆]²⁺ H₂O weakest of the three lowest B: [Ni(NH₃)₆]²⁺ NH₃ stronger than H₂O middle A: [Ni(en)₃]²⁺ en strongest: N donor and a chelate highest - So. The energy of absorption follows Δₒ: C < B < A, which is option (a).
The idea to keep. Same metal ion, same charge: energy absorbed follows the spectrochemical series. Stronger ligand, bigger Δₒ, higher energy and shorter wavelength absorbed.
Answer from the NTA final answer key. Solution by PrepWiser.