Question

What type of isomerism is exhibited by the complex $\left[ {{{Co}}{{\left( {{{N}}{{{H}}_3}} \right)}_5}{{Cl}}} \right]{{S}}{{{O}}_4}$?

Answer 1

As we know that isomers are the compounds having the same molecular formula, but having different arrangement of atoms. In coordination compounds, there are different types of isomerism taking place. Isomers are mainly divided into two-structural and stereoisomers.

Complete step by step solution:
As we have seen in various other compounds, coordination compounds also have isomers. Structural isomers are classified into ionization, linkage, solvate or hydrate and coordination isomers. While stereoisomers are classified into geometrical and optical isomers.
Stereoisomerism occurs when the ligands have the same bonds, but the orientations are different. When the ligands have different bonds, then it is said to have structural isomerism. Their classification is as given below:
Ionization isomerism
This has occurred due to the transfer of groups between the complex and the ions outside the coordination sphere.
E.g. $[{{Co}}{({{N}}{{{H}}_3})_5}{{Br}}]{{S}}{{{O}}_4}$ and $[{{Co}}{({{N}}{{{H}}_3})_5}{{S}}{{{O}}_4}]{{Br}}$
Hydrate isomerism
In this type of isomerism, there is a difference in the number of solvent ligands, i.e. water, and the counter ion. But it has the same chemical composition.
E.g. $[{{Cr}}{({{{H}}_2}{{O}})_6}]{{C}}{{{l}}_3},[{{Cr}}{({{{H}}_2}{{O}})_5}{{Cl}}]{{C}}{{{l}}_2}\cdot{{{H}}_2}{{O}}$
Linkage isomerism
This is related to ambidentate ligands. These ligands can bind in more than one place.
E.g. $[{{Co}}\left( {{{ONO}}} \right){({{N}}{{{H}}_3})_5}]{{Cl}},[{{Co}}({{N}}{{{O}}_2}){({{N}}{{{H}}_3})_5}]{{Cl}}$
Coordination isomerism
In this type of isomerism, there is a difference in the distribution of ligands between the positive and negative ions.
$[{{Co}}{({{N}}{{{H}}_3})_6}][{{Cr}}{\left( {{{CN}}} \right)_6}],[{{Cr}}{({{N}}{{{H}}_3})_6}][{{Co}}{\left( {{{CN}}} \right)_6}]$
The given compound is an example of ionization isomerism. In this compound, ${{Cl}}$ can be exchanged to outside the coordination sphere and ${{S}}{{{O}}_4}$ can be exchanged to inside the coordination sphere. Its isomer can be $\left[ {{{Co}}{{\left( {{{N}}{{{H}}_3}} \right)}_5}{{S}}{{{O}}_4}} \right]{{Cl}}$.

Note:
Isomers are usually different compounds having different physical properties like color, structure of crystal, melting point, etc. Ionization isomerism occurs because it forms different ions in solution.