Optical Isomerism in Complex Species

Complex species are formed when a central metal ion is surrounded by ligands. Optical isomerism occurs in complex species when they possess chiral ligands or have a chiral arrangement of ligands around the central metal ion. In order to determine which of the given complex species exhibit optical isomerism, we need to analyze the ligands present in each option.

[Co(en)3]3
- This complex contains three en (ethylenediamine) ligands.
- En ligands are chiral, as they possess a plane of symmetry only when the two nitrogens are not attached to different substituents.
- Therefore, this complex can exhibit optical isomerism.

[Co(en)2Cl2]
- This complex contains two en (ethylenediamine) ligands and two chloride ligands.
- En ligands are chiral, as explained above.
- However, the presence of two identical en ligands in a cis arrangement cancels out the chiral nature, resulting in a meso compound.
- Therefore, this complex does not exhibit optical isomerism.

[Co(NH3)3Cl3]
- This complex contains three ammonia ligands and three chloride ligands.
- Ammonia and chloride ligands are not chiral.
- Therefore, this complex does not exhibit optical isomerism.

[Co(en)(NH3)2Cl2]
- This complex contains one en (ethylenediamine) ligand, two ammonia ligands, and two chloride ligands.
- En ligands are chiral, as explained above.
- The presence of one en ligand in a cis arrangement with the other ligands allows for optical isomerism.
- Therefore, this complex exhibits optical isomerism.

Summary
Based on the analysis of the ligands present in each complex species, the ones that exhibit optical isomerism are:
- [Co(en)3]3
- [Co(en)(NH3)2Cl2]

These complexes have chiral ligands or a chiral arrangement of ligands, allowing for the existence of optical isomers.