Question

What type of coordination compounds show optical isomerism?

What type of complexes exhibit optical isomerism?

Answer 1

Optical isomerism occurs in coordination compounds with non-superimposable mirror images (enantiomers). These isomers rotate plane-polarised light in opposite directions; one is dextrorotatory (+), the other is levorotatory (–). 

The types of complexes that typically exhibit optical isomerism are:

1. Tetrahedral complexes with four different ligands are usually chiral because they don’t have symmetry and can’t be matched up with their mirror images.
   For example, Tetrahedral complexes with four different monodentate ligands. However, this type of optical isomerism is rarely observed in tetrahedral complexes because the ligands in these complexes are often labile, meaning they readily exchange, leading to rapid racemization (conversion of an enantiomer into a racemic mixture).
2. Octahedral complexes with bidentate ligands can create chiral structures if the ligands are arranged unevenly. If the ligands are arranged asymmetrically, the complex becomes chiral and exhibits optical isomerism.
   For example, [Cr(ox)₃]³⁻ (where “ox” is the oxalate ligand, \[\ce{C2O^2-_4}\]) can exist as two non-superimposable mirror images.
3. Some cis isomers in octahedral complexes (where ligands are adjacent) can be chiral, leading to optical isomerism.
   For example, the complex cis-[Co(en)₂Cl₂]⁺ (where “en” represents ethylenediamine) is optically active because the cis arrangement of the ligands results in a structure that is not superimposable on its mirror image.
   In contrast, trans-isomers of octahedral complexes are optically inactive because they possess a plane of symmetry.