# Why are hexamonodentate ligands optically inactive?

After encountering a lot of problems on optical isomerism of coordination compounds I have come to an idea that only complexes with polydentate or tridentate ligands shows optical isomerism. For example $\ce{[Co(en)3]^{3+}}$ shows optical isomerism but complexes such as those having platinum as the central atom and having six different monodentate ligands don't show optical isomerism. I have no trouble understanding why $\ce{[Co(en)3]^{3+}}$ shows optical isomerism but I am facing trouble finding out a reason for the second case.

The main question is why do complexes having monodentate ligands don't show optical isomerism?Any ideas?

• What is the exact species you are looking at? It's not really possible to say anything without knowing what you're talking about. – orthocresol Apr 28 '17 at 19:30
• @orthocresol I just have the doubt that why coordinate compounds having monodentate ligands don't show optical isomerism. – Pink Apr 29 '17 at 2:56
• Do you have an example of platinum coordinated to 6 different ligands? It would seem that such a molecule chiral. – Tyberius Apr 29 '17 at 3:50
• @Tyberius the example given in my book is $\ce{[Pt(NH3)(Br)(Cl)(I)(NO2)(py)]}$ – Pink Apr 29 '17 at 4:00
• The compound you stated does show optical isomerism. In fact, there will be 30 isomers! en.wikipedia.org/wiki/Octahedral_molecular_geometry – Saad Apr 29 '17 at 11:32