Structural isomers of hexaammineiron(III) hexacyanidocobaltate(III)
I have found the answer:


  In the following case:
  $$\ce{[Fe(NH_3)_3(CN)_3][Co(CN)_3(NH_3)_3]}$$
  Both the constituent entities are neutral and hence will exist independently, and thus will not form isomers of the original compound.