227.

Illustrate with an example of the following:
Linkage isomerism

Linkage isomerism: The compounds which have the same molecular formula but differ in the mode of attachment of a ligand to the metal atom or ion are called linkage isomers. For example, in NO₂^– ion, the nitrogen atom as well as the oxygen atom can donate their lone pairs. This gives rise to isomerism. If nitrogen donates its lone pair, one particular compound will be formed. On the other hand, if oxygen donates its lone pair, a different compound is obtained. If the bonding is through N, the ligand is named as nitro and if it is through O, it is named as nitrito.
NO₂^– nitro ONO^– nitritol
For example, two diffeent penta-amine cobalt(III) chlorides each containing the NO₂ group in the complex ion have been prepared. These are:

$$\begin{gathered} \underset{\mathrm{yellow} \mathrm{brown}}{\left[\mathrm{Co}({\mathrm{NH}}_3{)}_5 ({\mathrm{NO}}_2)\right]{\mathrm{Cl}}_2} \underset{\left(\mathrm{III}\right) \mathrm{chloride}}{\mathrm{Penta}-\mathrm{amine} \mathrm{nitro} \mathrm{cobalt}} \\ \left[\mathrm{Co}({\mathrm{NH}}_3{)}_5 (\mathrm{ONO})\right]{\mathrm{Cl}}_2 \underset{\left(\mathrm{III}\right) \mathrm{chloride}.}{ \mathrm{Penta}-\mathrm{amine} \mathrm{nitrito} \mathrm{cobalt}} \end{gathered}$$