Question

Observe the following complexes \[ [\text{Mn(CN)}_6]^{3-},\quad [\text{Fe(CN)}_6]^{3-},\quad [\text{Co(C}_2\text{O}_4)_3]^{3-},\quad [\text{MnCl}_6]^{3-},\quad [\text{Fe(CN)}_6]^{4-},\quad [\text{CoF}_6]^{3-} \] From the above, the number of inner orbital complexes with paramagnetic nature is:

• A. 2
• B. 1
• C. 3
• D. 4

Hint:

Paramagnetic inner orbital complexes arise with strong field ligands and unpaired electrons.

Answer 1

The Correct Option is A

Inner orbital complexes involve pairing in the lower energy \( t_{2g} \) orbitals (low spin). Ligands like \( \text{CN}^- \) and \( \text{C}_2\text{O}_4^{2-} \) are strong field ligands. Analyzing: - \( [\text{Mn(CN)}_6]^{3-} \): Mn\(^{3+} \) has 4 unpaired electrons, strong field → inner orbital → paramagnetic ✅ - \( [\text{Fe(CN)}_6]^{3-} \): Fe\(^{3+} \), low spin → 1 unpaired → inner orbital → paramagnetic ✅ - \( [\text{Co(C}_2\text{O}_4)_3]^{3-} \): strong field → diamagnetic ✖ - \( [\text{MnCl}_6]^{3-} \): weak field ligand → outer orbital ✖ - \( [\text{Fe(CN)}_6]^{4-} \): Fe\(^{2+} \), strong field → diamagnetic ✖ - \( [\text{CoF}_6]^{3-} \): weak field ligand → outer orbital ✖ Only first two are inner orbital and paramagnetic.