Question

BAL is a chelating agent used in treating heavy metal poisoning. It acts as a bidentate ligand. What types of linkage isomers are possible when BAL coordinates to a metal ion?

Short answer

BAL forms chelate with metal ion through two thiol groups, methylene (CH₂) thiol group and hydroxyl group, methine (CH₂) thiol and hydroxyl groups. Therefore, three linkage isomers are possible.

Step-by-step solution

First linkage isomer

A bidentate ligand has two donor atoms with respect to the central metal ion. First linkage isomer is possible with two thiol groups of BAL. The two sulphur atoms of thiol groups link with the metal ion forming the first type of linkage isomer.

Second linkage isomer

Second linkage isomer is possible with methylene (CH₂) thiol and hydroxyl groups of BAL. The sulphur atom of ‘methylene (CH₂₎’ thiol group and oxygen of hydroxyl group link with the metal ion forming the second type of linkage isomer.

Third linkage isomer

Third linkage isomer is possible with methine (CH₂) thiol and hydroxyl groups of BAL. The sulphur atom of ‘methine (CH)’ thiol group and oxygen of hydroxyl group link with the metal ion forming the third type of linkage isomer.