Q68 · CSIR-NET Chemistry, June 2011
Paper: CSIR-NET June 2011 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Coordination Chemistry – General · Marks: 2 · Difficulty: Hard
The correct order of LMCT energies is:
(a)$\mathrm{MnO}_{4}^{-}<\mathrm{CrO}_{4}^{2-}<\mathrm{VO}_{4}^{3-}$
(b)$\mathrm{MnO}_{4}^{-}>\mathrm{CrO}_{4}^{2-}>\mathrm{VO}_{4}^{3-}$
(c)$\mathrm{MnO}_{4}^{-}>\mathrm{CrO}_{4}^{2-}<\mathrm{VO}_{4}^{3-}$
(d)$\mathrm{MnO}_{4}^{-}<\mathrm{CrO}_{4}^{2-}>\mathrm{VO}_{4}^{3-}$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
LMCT energy rises as the metal becomes harder to reduce: Mn(VII) < Cr(VI) < V(V). Hence MnO₄⁻ (purple, lowest energy) < CrO₄²⁻ (yellow) < VO₄³⁻ (colourless, UV).
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