Isomerism in coordination compounds refers to the existence of two or more compounds with the same chemical formula but different arrangements of atoms or groups of atoms. There are two main types of isomerism in coordination compounds: structural isomerism and stereoisomerism.1. Structural Isomerism: This type of isomerism arises due to the differences in the connectivity or bonding between the central metal ion and the ligands. There are three subtypes of structural isomerism:a Coordination Isomerism: This occurs in mixed-ligand complexes where the ligands can exchange positions between the coordination spheres of two different metal ions. For example, [Co NH3 6][Cr CN 6] and [Cr NH3 6][Co CN 6] are coordination isomers.b Linkage Isomerism: This occurs when a ligand can bind to the central metal ion through different donor atoms. For example, [Co NH3 5 NO2 ]2+ and [Co NH3 5 ONO ]2+ are linkage isomers, where the nitrite ligand is bound through nitrogen in the first compound and through oxygen in the second compound.c Ionization Isomerism: This occurs when a ligand in the coordination sphere is replaced by an anionic ligand present outside the coordination sphere. For example, [Co NH3 5Br]SO4 and [Co NH3 5SO4]Br are ionization isomers.2. Stereoisomerism: This type of isomerism arises due to the differences in the spatial arrangement of ligands around the central metal ion. There are two subtypes of stereoisomerism:a Geometrical Isomerism: This occurs when the ligands have different relative positions in space. It is commonly observed in square planar and octahedral complexes. For example, in the square planar complex [Pt NH3 2Cl2], the two possible geometrical isomers are cis-[Pt NH3 2Cl2] with NH3 and Cl ligands adjacent to each other and trans-[Pt NH3 2Cl2] with NH3 and Cl ligands opposite to each other .b Optical Isomerism: This occurs when the coordination compounds are non-superimposable mirror images of each other, like our left and right hands. These isomers are called enantiomers and exhibit optical activity. For example, the octahedral complex [Co en 2 NH3 2]3+ where en is ethylenediamine exists as a pair of enantiomers, which are mirror images of each other and cannot be superimposed.In summary, isomerism in coordination compounds can be classified into structural isomerism coordination, linkage, and ionization isomerism and stereoisomerism geometrical and optical isomerism . These isomers differ in their connectivity or spatial arrangement of ligands around the central metal ion.