Question

Explain the purple colour of the complex, [Ti(H₂O)₆]³⁺ with the help of crystal field theory.

Answer 1

(1) [Ti(H₂O)⁶]³⁺ is an octahedral complex, oxidation state of titanium is +3 (Ti³⁺) and the coordination number is 6.

(2) Electronic configuration = ₂₂Ti [Ar]¹⁸ 3d² 4s²

Electronic configuration = Ti³⁺ [Ar]¹⁸ 3d¹

OR

1

(3) According to crystal field theory, 

3d orbitals undergo crystal field splitting giving higher energy e_g, two orbitals and lower energy t_2g, three orbitals.

Fig : Crystal field splitting in [Ti(H₂O)⁶]³⁺

(4) The crystal field splitting energy (CFSE),  

Δ₀ is found to be 3.99 x 10 J/ion from the spectrochemical studies.

(5) The absorption of radiation of wavelength λ or frequency v results in the transition of one unpaired electron from Photon energy t_2g orbital to e_g orbital. 

 

Fig : Photon absorption and the absorption spectrum of [Ti(H₂O)₆)³⁺

(6) The wavelength of the absorbed radiation will be.

(7) Hence,

The complex [Ti(H₂O)₆]³⁺ absorbs the green radiation of wavelength 498 nm in the visible region and transmits the complementary purple light. Therefore the complex is purple coloured.