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Colour of vanadium +5 vs +3 compounds

Short answer

V⁵⁺ is 3d⁰ with no d electrons, so no d–d transition can occur and it appears colourless. V³⁺ is 3d²; the two d electrons can undergo d–d transitions by absorbing visible light, giving coloured compounds.

Give reasons: The components formed by symbol 'V' element in +5 oxidation state are colourless but those formed in +3 oxidation state are colourful.

Colour in transition metal compounds is due to d–d transitions, which need at least one d electron.

  • V⁵⁺ has the configuration [Ar] 3d⁰. It has no d electron, so no d–d transition can occur and no visible light is absorbed. Such compounds show no colour from d–d transitions (any pale colour, as in V₂O₅, comes from charge transfer).
  • V³⁺ has the configuration 3d². The two d electrons can be excited from t₂g to e_g by absorbing visible light, so V(III) compounds are coloured (for example [V(H₂O)₆]³⁺ is green).

Hence V(III) compounds are coloured while d⁰ V(V) compounds are colourless.

✓ Answer checked by Claude Opus 5.5 (high effort)

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