Question

Give reason for the violet colour of the complex \( [\text{Ti(H}_2\text{O)} _6]^{3+} \) on the basis of crystal field theory.

Hint:

The colour of transition metal complexes is due to d-d transitions. The nature of ligands and the splitting energy \(\Delta\) determine the observed colour.

Answer 1

The violet colour arises due to the d-d electronic transition within the split d-orbitals.
Step 1: Electronic Configuration of \( [\text{Ti(H}_2\text{O)}_6]^{3+} \) For \( \text{Ti}^{3+} \), the electronic configuration is: \[ \text{Ti}^{3+} = 3d^1 \] Step 2: Crystal Field Splitting and d-d Transition In an octahedral field, the d-orbitals split into: \[ t_{2g} \quad \text{(lower energy)} \quad \text{and} \quad e_g \quad \text{(higher energy)} \] Since Ti\(^{3+}\) has one electron, it occupies the \( t_{2g} \) orbital as: \[ t_{2g}^1 e_g^0 \] Step 3: Cause of Violet Colour When visible light is absorbed, the electron gets excited from the \( t_{2g} \) to the \( e_g \) orbital, causing a d-d transition. The observed colour (violet) is due to the complementary colour of the absorbed wavelength.