Question

Which of the following system in an octahedral complex has maximum unpaired electrons?

• A. d⁹ (high spin)
• B. d⁶ (low spin)
• C. d⁴ (low spin)
• D. d⁷ (high spin)

Answer 1

The Correct Option is D

1. d9 (high spin):

• In an octahedral field, the d orbitals split into t2g (lower energy) and eg (higher energy) sets.¹
• d9 configuration: t2g6 eg3²
• Number of unpaired electrons: 1

2. d6 (low spin):

• d6 configuration (low spin): t2g6 eg0
• Number of unpaired electrons: 0

3. d4 (low spin):

• d4 configuration (low spin): t2g4 eg0³
• Number of unpaired electrons: 2

4. d7 (high spin):

• d7 configuration (high spin): t2g5 eg2
• Number of unpaired electrons: 3

Comparison:

• d9 (high spin): 1 unpaired electron
• d6 (low spin): 0 unpaired electrons⁴
• d4 (low spin): 2 unpaired electrons⁵
• d7 (high spin): 3 unpaired electrons⁶

Conclusion:

• The d7 (high spin) configuration has the maximum number of unpaired electrons (3).

The correct answer is Option 4.

Answer 2

Unpaired Electrons in Octahedral Complexes 

This document analyzes the number of unpaired electrons in different d-electron configurations within an octahedral field, considering both high-spin and low-spin cases.

1. d⁹ (High Spin)

In an octahedral field, the d orbitals split into $t_{2g}$ (lower energy) and $e_g$ (higher energy) sets.

d⁹ configuration: $t_{2g}^6 e_g^3$

Number of unpaired electrons: 1

2. d⁶ (Low Spin)

d⁶ configuration (low spin): $t_{2g}^6 e_g^0$

Number of unpaired electrons: 0

3. d⁴ (Low Spin)

d⁴ configuration (low spin): $t_{2g}^4 e_g^0$

Number of unpaired electrons: 2

4. d⁷ (High Spin)

d⁷ configuration (high spin): $t_{2g}^5 e_g^2$

Number of unpaired electrons: 3

Comparison

A summary of the number of unpaired electrons for each configuration:

• d⁹ (high spin): 1 unpaired electron
• d⁶ (low spin): 0 unpaired electrons
• d⁴ (low spin): 2 unpaired electrons
• d⁷ (high spin): 3 unpaired electrons

Conclusion

The d⁷ (high spin) configuration has the maximum number of unpaired electrons (3).

Therefore, Option 4 is the correct answer.