Question

Given below are two statements :
Statement I : [Mn(CN)$_6$]$^{3-}$, [Fe(CN)$_6$]$^{3-}$ and [Co(C$_2$O$_4$)$_3$]$^{3-}$ are d$^2$sp$^3$ hybridised.
Statement II : [MnCl$_6$]$^{3-}$ and [FeF$_6$]$^{3-}$ are paramagnetic and have 4 and 5 unpaired electrons, respectively.
Choose the correct option.

• A. Both statement I and statement II are true
• B. Both statement I and statement II are false
• C. Statement I is correct but statement II is false
• D. Statement I is incorrect but statement II is true

Hint:

Strong-field ligands (CN$^-$, CO) favor low-spin inner-orbital complexes, while weak-field ligands (F$^-$, Cl$^-$) produce high-spin outer-orbital complexes.

Answer 1

The Correct Option is A

Statement I:
- In all three complexes, the central metal ion is in +3 oxidation state. - CN$^-$ and C$_2$O$_4^{2-}$ act as strong-field ligands (especially with higher oxidation states). - Strong-field ligands cause electron pairing, allowing the use of inner d-orbitals.
[Mn(CN)$_6$]$^{3-}$ : Mn$^{3+}$ (3d$^4$), low-spin, inner-orbital complex → d$^2$sp$^3$
[Fe(CN)$_6$]$^{3-}$ : Fe$^{3+}$ (3d$^5$), low-spin → d$^2$sp$^3$
[Co(C$_2$O$_4$)$_3$]$^{3-}$ : Co$^{3+}$ (3d$^6$), low-spin → d$^2$sp$^3$
Hence, Statement I is true.
Statement II:
- Cl$^-$ and F$^-$ are weak-field ligands. - Weak-field ligands form high-spin complexes.
[MnCl$_6$]$^{3-}$ : Mn$^{3+}$ (3d$^4$) → 4 unpaired electrons
[FeF$_6$]$^{3-}$ : Fe$^{3+}$ (3d$^5$) → 5 unpaired electrons
Both complexes are paramagnetic with the stated number of unpaired electrons. Hence, Statement II is also true.
Therefore, the correct answer is (A).