JEE Advanced 2016 · Paper 1, Chemistry question 35

$\ce{[CoL2Cl2]^-}$ is an octahedral $\ce{M(AB)2a2}$ complex, with AB the unsymmetrical N,O-chelate.

Two Cl trans. The two chelates lie in the equatorial plane, with N trans to N or N trans to O: 2 isomers.

Two Cl cis. Each Cl is trans to a donor atom of a chelate:

• N trans N (O's trans to the Cl's): 1 isomer;
• O trans O (N's trans to the Cl's): 1 isomer;
• N trans O: 1 isomer.
  That is 3 isomers.

Total: 5 geometric isomers.

Answer: 5