Discuss the isomerism exhibited by coordination... - SS3 Chemistry Inorganic Chemistry: Periodic Trends and Properties Question

Isomerism is a fascinating phenomenon observed in coordination compounds, where different compounds have the same chemical formula but differ in their arrangement of ligands around the central metal ion. Isomerism in coordination compounds can be broadly categorised into two types: structural isomerism and stereoisomerism.

1.    Structural Isomerism:

a.    Ionisation Isomerism: In this type, ligands and counterions exchange places. For example, [Co(NH3)5Cl]Cl2 and [Co(NH3)5Cl2]Cl have the same chemical formula but differ in the arrangement of Cl and Cl2-.

b.    Coordination Isomerism: This occurs when ligands exchange places between the central metal ions in a complex. For instance, [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6] are coordination isomers.

2. Stereoisomerism:

a.    Geometric Isomerism (Cis-Trans Isomerism): It arises when ligands can be arranged differently around a coordination complex. Common in octahedral complexes with bidentate ligands, like [Pt(NH3)2Cl2], which can exist in cis and trans isomers.

b.    Optical Isomerism (Enantiomerism): This type of isomerism arises when a complex lacks a plane of symmetry and has non-superimposable mirror images (enantiomers). Enantiomers rotate plane-polarised light in opposite directions. For example, [Co(en)3]3+ exists as two enantiomers, which are mirror images of each other.

The importance of isomerism in coordination chemistry lies in its significant impact on the physical and chemical properties of coordination compounds. Isomers often exhibit different colours, solubilities, and reactivities. This property is exploited in various applications, such as in pharmaceuticals, where isomers may exhibit varying biological activities. Understanding isomerism is crucial in designing coordination compounds with specific desired properties and functionalities.