- 2072 Asoj · 2.5 marks
Colour of Ti³⁺ vs Ti⁴⁺ compounds
Short answer
Ti(III) is 3d1, so a d–d transition absorbs visible light, giving a violet colour. Ti(IV) is 3d0 with no d electrons, so no d–d transition occurs and compounds are colourless.
Explain why: Compounds of Titanium in +3 oxidation state are coloured but those in +4 oxidation state are colourless.
Colour in transition metal compounds comes from d–d transitions: an electron in a lower-energy d orbital absorbs visible light and jumps to a higher-energy d orbital of the split d set.
- Ti³⁺ has the configuration 3d¹. In water it forms [Ti(H₂O)₆]³⁺ with the single electron in a t₂g orbital. It absorbs light (about 500 nm, green–yellow) and jumps to e_g, so the complex looks violet (purple).
- Ti⁴⁺ has the configuration 3d⁰. There is no d electron to excite, so no d–d transition is possible and no visible light is absorbed. Its compounds (TiO₂, TiCl₄) are colourless or white.
Hence Ti(III) compounds are coloured and Ti(IV) compounds are colourless.
✓ Answer checked by Claude Opus 5.5 (high effort)
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