# What are the isomers of a complex having a structure of M(AB)2C2?

Our instructor have us answer an isomerism problem of a crystal structure that has a form of $$\ce{M(AB)2C2}$$. I keep getting 9 isomers, which includes the optically inactive isomer, and my peers and I have different answers.

• I thought of several wrong ways to count isomers, and still failed to get 5. If you want us to tell which of your isomers is wrong or which one is missing, then we really need to know more. – Ivan Neretin Jun 19 '19 at 11:10
• After more fiddling I succeeded in getting 5. If your peers are getting more, they must be counting enantiomers. – Ivan Neretin Jun 19 '19 at 11:23
• Sorry, but I have noticed that 4 of my isomers have D and L forms so instead of 5, the isomers that I have is 9 including the one which is the optically inactive isomer. – Kent de los Reyes Jun 19 '19 at 11:25
• Great. (Or maybe not.) Now you are ahead of me, because I'm getting 8, of which two are optically inactive. – Ivan Neretin Jun 19 '19 at 11:26
• How did you form another optically inactive isomer? I am new to this topic that's why I can't trust my intuitions. – Kent de los Reyes Jun 19 '19 at 11:31