Do either cis-#[3Co(en)_2Cl_2]^+# or trans-#[3Co(en)_2Cl_2]^-# have optical isomers?
The cis complex does support optical isomerism, (I take it you mean
The trans complex has planar symmetry. The cis complex, however, can support optical isomerism in that the ethylenediamine ligands cannot coordinate across 2 trans positions. I could not find an image on the webs to illustrate this isomerism, I suggest you consult a text of inorganic chemistry. When the 2 chloro ligands are cis, 2 non-superposable optical isomers result.