Question

The hybridization and magnetic nature of [Mn(CN)$_6$]$^{4-}$ and [Fe(CN)$_6$]$^{3-}$, respectively are :

• A. d$^2$sp$^3$ and paramagnetic
• B. sp$^3$d$^2$ and diamagnetic
• C. d$^2$sp$^3$ and diamagnetic
• D. sp$^3$d$^2$ and paramagnetic

Hint:

Strong field ligands (like $CN^-, CO, NO^+$) force electrons to pair up, often leading to inner orbital complexes ($d^2$sp$^3$). Always check for unpaired electrons after pairing to determine magnetic nature.

Answer 1

The Correct Option is A

Step 1: Both $Mn^{2+}$ ($3d^5$) and $Fe^{3+}$ ($3d^5$) have 5 electrons in the $d$-orbital.
Step 2: $CN^-$ is a strong field ligand, causing pairing.
Step 3: In a $d^5$ system with strong field pairing, 4 electrons pair up into two orbitals, leaving 1 electron unpaired in the third $t_{2g}$ orbital.
Step 4: Two $3d$ orbitals become vacant, allowing for d$^2$sp$^3$ (inner orbital) hybridization.
Step 5: Due to the 1 unpaired electron in both complexes, both are paramagnetic.