Unit 9 Coordination Compounds (Intext Questions-2)
Intext Questions
9.3 Indicate the types of isomerism exhibited by the following complexes and draw the structures for these isomers:
(i) $\mathrm{K}[\mathrm{Cr}\mathrm{(H_2O)_2}\mathrm{(C_2O_4)_2}]. $
(ii) $\left[\mathrm{Co}(\mathrm{en})_3\right] \mathrm{Cl_3}$
(iii) $\left[\mathrm{Co}\left(\mathrm{NH_3}\right)_5\left(\mathrm{NO_2}\right)\right]\left(\mathrm{NO_3}\right)_2$
(iv) $\left[\mathrm{Pt}\left(\mathrm{NH_3}\right)\left(\mathrm{H_2} \mathrm{O}\right) \mathrm{Cl_2}\right]$
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Answer
i. Both geometrical (cis-, trans-) isomers for $\mathrm{K}[\mathrm{Cr}\mathrm{(H_2O)_2}\mathrm{(C_2O_4)_2}]$ can exist. Also, optical isomers for cis-isomer exist.
Geometrical isomers 
Trans-isomer is optically inactive. On the other hand, cis-isomer is optically active.
(ii) Two optical isomers for $[\mathrm{CO(en)_3}]\mathrm{Cl_3}$
Two optical isomers are possible for this structure.
(iii) $[\mathrm{CO}\mathrm{(NH_3)_5}\mathrm{(NO_2)}]\mathrm{(NO_3)_2}$
A pair of optical isomers:
It can also show linkage isomerism.
$[\mathrm{CO}\mathrm{(NH_3)_5}\mathrm{(NO_2)}]\mathrm{(NO_3)_2} \text { and }[\mathrm{CO}\mathrm{(NH_3)_5}\mathrm{(ONO)}]\mathrm{(NO_3)_2}$
It can also show ionization isomerism.
$\left[\mathrm{CO}\mathrm{(NH_3)_5}\mathrm{(NO_2)}\right]\mathrm{(NO_3)_2} \quad \quad [\mathrm{CO(NH_3)_5(NO_3)(NO_3)(NO_2)}] $
(iv) Geometrical (cis-, trans-) isomers of $\left[\mathrm{Pt}\left(\mathrm{NH_3}\right)\left(\mathrm{H_2} \mathrm{O}\right) \mathrm{Cl_2}\right]$ can exist.
Cis $\quad \quad \quad$ Trans
9.4 Give evidence that $\left[\mathrm{Co}\left(\mathrm{NH_3}\right)_5 \mathrm{Cl}\right] \mathrm{SO_4}$ and $\left[\mathrm{Co}\left(\mathrm{NH_3}\right)_5\left(\mathrm{SO_4}\right)\right] \mathrm{Cl}$ are ionisation isomers.
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Answer
When ionization isomers are dissolved in water, they ionize to give different ions. These ions then react differently with different reagents to give different products.
$ \left[\mathrm{CO}\left(\mathrm{NH_3}\right)_{5} \mathrm{Cl}\right] \mathrm{SO_4}+\mathrm{Ba}^{2+} \longrightarrow \underset{\text{White precipitate}}{\mathrm{BaSO_4} \downarrow} $
$\left[\mathrm{CO}\left(\mathrm{NH_3}\right)_{5} \mathrm{Cl}\right] \mathrm{SO_4}+\mathrm{Ag}^{+} \longrightarrow$ No reaction
$ {\left[\mathrm{CO}\left(\mathrm{NH_3}\right)_{5} \mathrm{SO_4}\right] \mathrm{Cl}+\mathrm{Ba}^{2+} \longrightarrow \text { No reaction }} $
$ [\mathrm{CO}(\mathrm{NH_3})_{5} \mathrm{SO_4}] \mathrm{Cl}+\mathrm{Ag}^{+} \longrightarrow \underset{\text{White precipitate }}{\mathrm{AgCl} \downarrow} $
