# Why are complexes of type MA3B3 not optical active?

Complexes of type $$\ce{MA3B3}$$ have two geometrical isomers, namely:

1. fac-isomer
2. mer-isomer

If we look closely at the mer-isomer, it has a plane of symmetry, so it is optically inactive. But the fac-isomer has no plane of symmetry. Still, it is optically inactive, why?

Being a 12th grader, I wonder where am I wrong in my understanding of optical isomerism in coordination complexes.

• Because of three planes of symmetry, to begin with. Mar 1, 2021 at 7:55
• There is no plane of symmetry in fac-isomer of type ${MA_3B_3}$ Mar 1, 2021 at 8:23
• Your assertiveness is not quite justified. Mar 1, 2021 at 8:30
• there is a plane of symmetry in the fac- along the axis AMB and between two A and two B atoms. see the image here courses.lumenlearning.com/introchem/chapter/…. Mar 1, 2021 at 8:31
• chemtube3d.com/symfecl3br3fac Mar 2, 2021 at 17:13

Because you could have chosen any of three A atoms in your view there are three mirror planes, which pass through a common rotation axis. The axis passes through the face that has all A atoms at its corners and the opposite face which has all B atoms. This symmetry is called $$C_{\mathrm{3v}}$$ in the language of point groups.