Chemistry query - Cahn-Ingold-Prelog system for octahedral complexes

[pkgem]

Hi all,

 

I'm trying to answer an assignment question that asks me to draw and name the isomers of a particular transition-metal complex and then identify the number of chemically inequivalent telluriuim atoms in the isomers.

 

So far, so good except for I'm a little confused with regards to my nomenclature for the transition-metal complex that I have. It's octahedral and contains only two distinct ligands: in other words, it has two sets of three identical ligands. Thus, it fits nicely with the fac/mer system of naming - I can identify that it can have both facial and meridional isomers. What I'm not sure about is whether I can (and should) apply the Cahn-Ingold-Prelog system also. The CIP system for octahedral complexes starts by saying I have to identify the priority 1 ligand - however, as I have sets of identical ligands, I have three priority 1 ligans. So, which do I choose? Or is it unecessary and I only need to apply the fac/mer system?

 

In summary: Can the CIP system be applied for octahedral metal complexes that don't have six non-identical ligands?

 

Any help would be appreciated. It doesn't directly answer my assignment question but it helps me to understand a part of it. So, thanks in advance.

 

Gem