Describe the Jahn-Teller Effect (NEET Chemistry)

Hint: The Jahn-Teller effect pertains to the distortion of a nonlinear molecular system. It accounts for the decrease in symmetry and energy of the system. This effect arises from the varying degrees of interaction between the ligands and the metal’s d orbitals.

Complete answer:

A nonlinear molecular system experiences distortion, which leads to a reduction in both its symmetry and energy. This phenomenon is called the Jahn-Teller effect.

In octahedral complexes, the axial bond lengths may differ from the equatorial bond lengths, showing the Jahn-Teller effect. The axial bond lengths can be either longer or shorter than the equatorial bond lengths. The Jahn-Teller effect is also observed in tetrahedral complexes. This effect is influenced by the electronic state of the system.

Consider a nonlinear complex. If the electronic configuration in the ground state has degenerate orbitals, the complex will distort to remove this degeneracy and achieve a lower energy state.

In an octahedral field, the metal’s d orbitals split into two energy levels: [latex]t_{2g} [/latex] and [latex] \text{e}_g  [/latex]. The [latex]t_{2g} [/latex] orbitals are lower in energy and oriented between the axes, avoiding direct interaction with the approaching ligands. The [latex] \text{e}_g  [/latex] orbitals, which are higher in energy, are aligned along the axes, directly facing the incoming ligands.

The interaction between ligands and [latex] \text{e}_g  [/latex] orbitals is greater than that between ligands and [latex]t_{2g} [/latex] orbitals, high spin [latex] \text{d}^4 [/latex], low spin [latex] \text{d}^7 [/latex] and [latex] \text{d}^9 [/latex]configurations have greater Jahn Teller effect.

Note: In high-spin [latex] \text{d}^4 [/latex] octahedral complexes of Cr²⁺ and Cu²⁺, the Jahn-Teller effect occurs as the lone pair of electrons causes the degenerate [latex] \text{e}_g  [/latex] level to split into the [latex]\ d_{z^2}[/latex] and  [latex] \ d_{x^2 – y^2} [/latex] orbitals.