Question

The Crystal Field Theory (CFT) of coordination compounds is based on the effect of different crystal fields (provided by the ligands taken as point charges) on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. In tetrahedral coordination entity formation, the d-orbital splitting is smaller as compared to the octahedral entity.
On the basis of CFT, explain why [Ti(H$_2$O)$_6$]Cl$_3$ complex is coloured? What happens on heating the complex [Ti(H$_2$O)$_6$]Cl$_3$? Give reason.

Hint:

Colour in coordination compounds arises from the splitting of d-orbitals in the presence of ligands, and this splitting depends on the geometry and nature of the ligands.

Answer 1

The [Ti(H$_2$O)$_6$]Cl$_3$ complex is coloured due to the splitting of the d-orbitals of the Ti$^{3+}$ ion in the presence of the ligands. When ligands surround the metal ion, they create an electrostatic field that splits the degenerate d-orbitals into different energy levels. The absorption of specific wavelengths of light excites electrons from the lower to the higher d-orbital level, resulting in colour. On heating, the ligands may be replaced or the electronic configuration may change, causing the absorption spectrum to shift, thus altering the colour of the complex.