Question

Among the following complexes, the one which shows zero crystal field stabilization energy (CFSE) is:

• A. $\left[Mn\right(H_{2}O{)}_6{]}^{3+}$
• B. $\left[Fe\right(H_{2}O{)}_6{]}^{3+}$
• C. $\left[Co\right(H_{2}O{)}_6{]}^{2+}$
• D. $\left[Co\right(H_{2}O{)}_6{]}^{3+}$

Answer 1

The correct option is B $\left[Fe\right(H_{2}O{)}_6{]}^{3+}$

$H_{2}O$ is a weak field ligand, hence ${\Delta }_o<\text{pairing energy}$
$CFSE=(-0.4x+0.6y){\Delta }_o$
Where, $x$ and $y$ are number of electrons occupying $t_{2g}$ and $e_g$ orbitals respectively.
For, $Fe(H_{2}O{)}_6{]}^{3+}$ complex ion,
$F{e}^{3+}\left(3d^5\right)=t_{2g}^3{e}_g^2=0.4\times 3+0.6\times 2=0.0=0.0{\Delta }_o$