Q.Explain optical isomerism in coordination compounds with an example.

Step 1. Coordination compounds that possess chirality (lack an internal mirror plane) exhibit optical isomerism, exactly as chiral organic molecules do.

Step 2. A pair of optically active isomers that are non-superimposable mirror images of one another are called enantiomers.

Step 3. Their solutions rotate the plane of plane-polarised light either clockwise or anticlockwise, and the corresponding isomers are labelled 'd' (dextrorotatory) and 'l' (levorotatory) respectively.

Step 4. Octahedral complexes of the type [M(xx)₃] (three identical symmetric bidentate ligands) are a classic case: [Co(en)₃]³⁺ (Figure 5.7) has three 'en' (ethane-1,2-diamine) ligands wrapped around cobalt in a propeller-like arrangement, and this arrangement can twist either left-handed or right-handed, giving two structures that are genuine, non-superimposable mirror images of each other -- the d- and l-[Co(en)₃]³⁺ enantiomers. …

Define optical isomerism through chirality and the enantiomer/mirror-image relationship, and illustrate with the …

• Confusing optical isomerism (non-superimposable mirror images, requires chirality) with geometrical isomerism (cis/trans, a completely different spatial relationship not necessarily involving mirror images). …