# For a structure of a compouund optically active, what is the number of stereo isomers if no geometrical isomers are present?

Suppose for example the compounds $$\ce{M(AA)3}$$ and $$\ce{M(AA)3bc}$$, with $$\ce{M}$$, the central metal atom and $$\ce{AA}$$, a bidentate ligand.

What is the total number of stereo-isomers of both?

I was taught that for the compound $$\ce{M(AA)3}$$ the number of stereo isomers is 2; there are no geometric isomers and one is optically active. For $$\ce{M(AA)3bc}$$, the total of stereo isomers is 3.

If

$$\text{number of stereo isomers} = \text{number of geometric isomers} +\text{number of optical isomers}$$

then why the total of stereo isomers is 2 for $$\ce{M(AA)3}$$ if only one structure is optically active, while the above formula stands good for $$\ce{M(AA)3bc}$$?