Question

Jahn-Teller effect is not observed in high spin complexes of

• A. $d^7$
• B. $d^8$
• C. $d^4$
• D. $d^9$

Answer 1

The Correct Option is B

 The Jahn-Teller effect is an important concept in coordination chemistry that is observed in octahedral complexes. It involves a geometrical distortion of the complex that reduces its symmetry and often leads to a more stable system. The Jahn-Teller effect typically occurs when there are degenerate orbitals (orbitals of the same energy) in a coordination complex and there is an uneven distribution of electrons in these orbitals.

The question asks us which of the given configurations does not exhibit the Jahn-Teller effect in high spin complexes.

1. The electronic configuration for \(d^7\) in a high spin octahedral field can be represented as \(t_{2g}^5e_g^2\). Here, there are no degenerate orbitals with unequal electron distribution, thus Jahn-Teller distortion is not prominently observed.
2. For \(d^8\), in a high spin complex, the configuration would be \(t_{2g}^6e_g^2\). In this case, both \(e_g\) orbitals have an equal distribution of electrons, hence there is no Jahn-Teller effect. This explains why \(d^8\) complexes do not show Jahn-Teller distortion.
3. In \(d^4\) high spin complexes, the configuration is \(t_{2g}^3e_g^1\). The single electron in the \(e_g\) level can cause significant Jahn-Teller distortion due to the unequal filling of these orbitals.
4. For \(d^9\) complexes, the configuration is \(t_{2g}^6e_g^3\). Here, the \(e_g\) level is unevenly populated with three electrons, making it prone to Jahn-Teller distortion.

In conclusion, among the given configurations, \(d^8\) high spin complexes do not show the Jahn-Teller effect because they do not have unsymmetrically filled degenerate orbitals.

Configuration	High Spin	Jahn-Teller Effect
\(d^7\)	\(t_{2g}^5e_g^2\)	No significant distortion
\(d^8\)	\(t_{2g}^6e_g^2\)	No distortion
\(d^4\)	\(t_{2g}^3e_g^1\)	Shows distortion
\(d^9\)	\(t_{2g}^6e_g^3\)	Shows distortion