Arrange the following Cobalt
Question:

Arrange the following Cobalt complexes in the order of increasing Crystal Field Stabilization Energy (CFSE) value.

Complexes : $\left[\underset{\mathrm{A}}{\mathrm{CoF}_{6}}\right]^{3-},\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+},\left[\underset{\mathrm{B}}{\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}}\right]^{3+}$ and $\left[\mathrm{Co}(\mathrm{en})_{3}\right]^{3+}$

Choose the correct option :

  1. $\mathrm{A}<\mathrm{B}<\mathrm{C}<\mathrm{D}$

  2. $B<A<C<D$

  3. $\mathrm{B}<\mathrm{C}<\mathrm{D}<\mathrm{A}$

  4. $C<D<B<A$


Correct Option: , 2

Solution:

(i) CFSE $\propto$ charge or oxidation no. of central metal ion.

(ii) $\mathrm{CFSE} \propto$ strength of ligand

$\mathrm{en}>\mathrm{NH}_{3}>\mathrm{H}_{2} \mathrm{O}>\mathrm{F}^{-}$

$\therefore$ order of CFSE

$\left.\left[\mathrm{Co}(\mathrm{en})_{3}\right]^{+3}>\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{+3}>\left[\mathrm{CoF}_{6}\right]^{-3}>\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{+2}$

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