Q.Draw all possible geometrical isomers of the complex [Co(en)₂Cl₂]⁺ and identify the optically active isomer.

Step 1. [Co(en)₂Cl₂]⁺ is an octahedral [M(xx)₂B₂] type: 2 bidentate en ligands (4 N donor atoms) + 2 monodentate Cl ligands, on Co³⁺.

Step 2. Per Section 5.5.3, this exact complex has three stereoisomers total: geometrically, the two Cl ligands can sit adjacent to each other (cis) or opposite each other (trans).

Step 3. The TRANS isomer has an internal mirror plane (the two en rings arranged symmetrically about the Cl-Co-Cl axis) and is therefore superimposable on its own mirror image -- optically inactive (achiral), a single isomer.

Step 4. The CIS isomer lacks such an internal mirror plane -- it is chiral, and exists as a pair of non-superimposable mirror images (enantiomers), giving TWO distinct, optically active cis forms (labelled d- and l-cis). …

Identify [Co(en)₂Cl₂]⁺ as the chapter's own worked [M(xx)₂B₂] example (Figure 5.8), draw the cis and trans arrangements of the two Cl ligands, a …

• Assuming there are only two isomers (cis and trans) and missing that the cis form itself splits into a pair of non-superimposable mirror-image enantiomers. …