Q10 · CSIR-NET Chemistry, June 2021

Paper: CSIR-NET June 2021 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Charge Transfer Spectra · Marks: 2 · Difficulty: Medium

For the ligand-to-metal charge-transfer (LMCT) transitions in the oxo-anions given below, the wavelength of the transitions are in the order
(a)$\mathrm{VO}_{4}^{3-}<\mathrm{CrO}_{4}^{2-}<\mathrm{MnO}_{4}^{-}$and $\mathrm{WO}_{4}^{2-}<\mathrm{MoO}_{4}^{2-}<\mathrm{CrO}_{4}^{2-}$
(b)$\mathrm{VO}_{4}^{3-}<\mathrm{CrO}_{4}^{2-}<\mathrm{MnO}_{4}^{-}$and $\mathrm{WO}_{4}^{2-}>\mathrm{MoO}_{4}^{2-}>\mathrm{CrO}_{4}^{2-}$
(c)$\mathrm{VO}_{4}^{3-}>\mathrm{CrO}_{4}^{2-}>\mathrm{MnO}_{4}^{-}$and $\mathrm{WO}_{4}^{2-}<\mathrm{MoO}_{4}^{2-}<\mathrm{CrO}_{4}^{2-}$
(d)$\mathrm{VO}_{4}^{3-}>\mathrm{CrO}_{4}^{2-}>\mathrm{MnO}_{4}^{-}$and $\mathrm{WO}_{4}^{2-}>\mathrm{MoO}_{4}^{2-}>\mathrm{CrO}_{4}^{2-}$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
LMCT shifts to longer λ as the metal becomes more oxidising: VO₄³⁻ < CrO₄²⁻ < MnO₄⁻; down the group it shifts to shorter λ: WO₄²⁻ < MoO₄²⁻ < CrO₄²⁻ (a).

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