MCQ
Among the following complexes the one which shows zero crystal field stabilization energy $(CFSE)$ is
- A$[Mn(H_2O)_6]^{3+}$
- ✓$[Fe(H_2O)_6]^{3+}$
- C$[Co(H_2O)_6]^{2+}$
- D$[Co(H_2O)_6]^{3+}$
✓
Answer
Correct option: B.
$[Fe(H_2O)_6]^{3+}$
b
$\mathrm{H}_{2} \mathrm{O}$ is a weak field ligand, hence
$\mathrm{H}_{2} \mathrm{O}$ is a weak field ligand, hence
$\Delta_{o}<$ pairing energy.
$\mathrm{CFSE}=(-0.4 x+0.6 y) \Delta_{o}$
where, $x$ and $y$ are no. of electrons occupying $t_{2 g}$ and es orbitals respectively.
For $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ complex ion.
$\mathrm{Fe}^{3+}\left(3 d^{5}\right) =t_{2 \mathrm{g}}^{3} e_{\mathrm{g}}^{2}=-0.4 \times 3+0.6 \times 2$
$=0.0 \text { or } 0\; \mathrm{Dq}$
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