Question

What type of structural isomer are \[[Co{(N{H_3})_5}Br]S{O_4}\] and \[[Co{(N{H_3})_5}S{O_4}]Br\]? Give the chemical test to distinguish the isomers?

Answer 1

Hint: In order to find what type of structural isomer present in \[[Co{(N{H_3})_5}Br]S{O_4}\] and \[[Co{(N{H_3})_5}S{O_4}]Br\], we must first know what is a structural isomer and types of structural isomers.
- Structural isomer is also known as the constitutional isomer.


Complete Solution :
Let us first understand what an isomerism is. Isomers are compounds that have the same molecular formula but different structures and therefore they have different chemical and physical properties. The phenomenon of the existence of such a compound is called isomerism.
Isomerism can be classified into two types:
- Structural isomerism
- Stereoisomerism
When the atoms in the molecule and the functional groups are arranged in different ways, it is known as structural isomerism. Structural isomerism is also known as constitutional isomerism.

Let us now come to the question:
- The type of structural isomer present in \[[Co{(N{H_3})_5}Br]S{O_4}\] and \[[Co{(N{H_3})_5}S{O_4}]Br\] is the ionisation isomer. Ionisation isomerism will arise due to the difference in the position of the atoms or group within or outside the coordination sphere.
- The compound \[[Co{(N{H_3})_5}Br]S{O_4}\] is red-violet in colour and will form precipitate with \[BaC{l_2}\]indicating that \[SO_4^{2 - }\] ion is outside the coordination sphere.
\[[Co{(N{H_3})_5}Br]S{O_4} \rightleftharpoons {[Co{(N{H_3})_5}Br]^{2 + }} + SO_4^{2 - }\]
\[{\text{BaC}}{{\text{l}}_{\text{2}}}{\text{ + SO}}_{\text{4}}^{{\text{2 - }}} \to {\text{BaS}}{{\text{O}}_{\text{4}}} \downarrow {\text{(white ppt) + 2C}}{{\text{l}}^{\text{ - }}}\]

- The compound \[[Co{(N{H_3})_5}S{O_4}]Br\] is red and it will not form precipitate with \[BaC{l_2}\]. It will form a precipitate of \[AgBr\] with \[AgN{O_3}\], indicating that \[B{r^ - }\] is outside the coordination sphere.

\[[Co{(N{H_3})_5}S{O_4}]Br \rightleftharpoons {[Co{(N{H_3})_5}S{O_4}]^ + } + B{r^ - }\]
\[{\text{AgN}}{{\text{O}}_{\text{3}}} + B{r^ - } \to {\text{AgBr}} \downarrow {\text{ + NO}}_3^ - \]
Therefore, the type of structural isomer present in \[[Co{(N{H_3})_5}Br]S{O_4}\] and \[[Co{(N{H_3})_5}S{O_4}]Br\] is the ionisation isomer.

Additional information:
Stereoisomerism is present in the compounds having the same chemical formula but different orientation of the atoms. There are two types of stereoisomerism, they are:
- Geometrical isomerism
Geometrical isomerism is due to the ligands occupying different positions around the central metal ions. Geometrical isomerism is also known as Cis-trans isomerism.
- Optical isomerism:
Optical isomerism will occur in substances that have the same molecular formula and chemical properties, but cannot be superimposed on each other.

Note: The structural isomerism other than ionisation isomerism are:
- Hydrate isomerism
- Coordination isomerism
- Linkage isomerism
- Coordination position isomerism.