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

Options

A. `d^(7)`
B. `d^(8)`
C. `d^(4)`
D. 2-)`

Explanation

To determine in which high spin complexes the Jahn-Teller effect is not observed, we can analyze the electron configurations of different d-electron counts in octahedral complexes. The Jahn-Teller effect occurs due to the unsymmetrical filling of the d-orbitals, particularly T2G and EG orbitals, which leads to distortion in the geometry of the complex.

### Step-by-Step Solution:

1. **Understanding the Jahn-Teller Effect**:
- The Jahn-Teller effect is a phenomenon observed in certain coordination complexes where the geometry of the complex distorts due to the uneven distribution of electrons in the d-orbitals. This effect is typically seen in octahedral complexes with an uneven number of electrons in the d-orbitals.

2. **Identifying High Spin Complexes**:
- High spin complexes are formed when weak field ligands are present, leading to less pairing of electrons. In these complexes, electrons occupy the higher energy orbitals before pairing occurs.

3. **Analyzing Different d-Electron Counts**:
- **D7 Configuration**:
- In a D7 high spin complex, the electron filling would be: T2G (3 electrons) and EG (4 electrons). The filling is unsymmetrical (3 in T2G and 4 in EG), leading to distortion. Thus, the Jahn-Teller effect is observed.
- **D8 Configuration**:
- In a D8 high spin complex, the electron filling is: T2G (6 electrons) and EG (2 electrons). The filling is symmetrical (3 in T2G and 2 in EG), meaning there is no unsymmetrical filling. Therefore, the Jahn-Teller effect is **not** observed.
- **D4 Configuration**:
- In a D4 high spin complex, the filling would be: T2G (3 electrons) and EG (1 electron). Here, T2G is fully filled and EG is unsymmetrically filled (1 in EG and 1 empty), leading to distortion. Thus, the Jahn-Teller effect is observed.

4. **Conclusion**:
- From the analysis, we can conclude that the Jahn-Teller effect is not observed in high spin complexes of D8 configuration.

### Final Answer:
The Jahn-Teller effect is not observed in high spin complexes of **D8**.