Question

What are linkage isomers? Give an example.

Answer 1

Hint : Isomers in chemistry are molecules or polyatomic ions that have the same molecular formula, that is, the same number of atoms of each element but different atomic arrangements in space. Isomerism refers to the existence or potential of isomers. Isomers don't always have the same chemical or physical properties as one another.

Complete Step By Step Answer:
Two or more coordination compounds in which at least one of the ligands has a different donor atom are called linkage isomers. Only when a compound contains a ligand that can bind to the metal atom in two (or more) different ways can this type of isomerism occur. When ambidentate ligands are capable of coordinating in multiple ways, linkage isomerism occurs.
Thiocyanate, $SCN$ , is another example of an ambidentate ligand, as it can attach to either the sulfur or nitrogen atom. Linkage isomerism is caused by such compounds. Typical ligands that produce linkage isomers include thiocyanate, $SCN{{\text{ }}^{-}}$ , and isothiocyanate, $NCS$ ; selenocyanate, $SeCN$ , and iso selenocyanate, $SCN{{\text{ }}^{-}}$ ; and selenocyanate, $SeC{{N}^{-}}$ and iso selenocyanate, $NCSe$ .
The formula $\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}\left( NO2 \right) \right]C{{l}_{2}}$ was the first reported example of linkage isomerism. There are two separable linkage isomers of the cationic cobalt complex. The nitro ligand is bound through nitrogen in the yellow-colored isomer. The nitrate is bound through one oxygen atom in the red linkage isomer. ${{\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}\left( ONO \right) \right]}^{2+}}$ is a common abbreviation for the O-bonded isomer.
The structural difference between the isomers was only explained in 1907, even though their existence had been known since the late 1800s. It was later discovered that UV-irradiation converted the red isomer to the yellow isomer. In this case, an intramolecular rearrangement results in the formation of the nitro isomer $\left( Co-N{{O}_{2}} \right)$ from the nitrite isomer $\left( Co-ONO \right)$ .

Note :
Constitutional isomerism is a term used to describe structural isomerism. The functional groups and atoms in these isomers' molecules are linked in various ways. Because structural isomers may or may not contain the same functional group, they are given different IUPAC names.