The uv-visible absorption spectra of some titanium complex ions and compounds

The uv-visible absorption spectrum for the hexaaquatitanium(III) ion, [Ti(H₂O)₆]³⁺(aq), shows a λ_max of ~520 nm, with strong absorption in the blue-green-yellow region, but little absorption in the violet and red regions, resulting in the ion being a purple in aqueous solution from a combination of violet and red (often quoted as violet in colour).

Note the strong absorption in the 'invisible' ultraviolet region <380 nm).

The electronic level field splitting diagram above shows the promotion of an electron by a visible light photon from the 3d ground state to the upper level of the 3d orbitals.

For more details see The chemistry of titanium

 

A solution of the hexaaquatitanium(II) ion, [Ti(H₂O)₆]²⁺(aq) is violet.

(I couldn't find a uv-visible absorption spectrum for the hexaaquatitanium(II)

The electronic situation is slightly different than the hexaaquatitanium(III) ion, [Ti(H₂O)₆]³⁺(aq) ion, giving a different  ∆E_elec, but visible light photons still provide the necessary excitation energy.

 

As a result, titanium(IV) oxide, TiO₂ (titanium dioxide), is a white solid from the reflectance of most visible light photons.

Titanium(IV) chloride,TiCl₄, is a colourless covalent liquid, tetrahedral in shape - four chloride ions effectively acts a four electron pair donating ligands.

Hydrated TiO₂ dissolves in conc. hydrofluoric acid to give a colourless solution of the hexafluorotitanate(IV) ion, an octahedral shaped complex with the formula [TiF₆]^2-(aq).

The hexachlorotitanate(IV) ion, is another octahedral shaped complex with the formula [TiCl₆]^2-(aq) also exists, but is apparently pale yellow.

For more details see The chemistry of titanium

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