Total number of all possible optical isomers of an octahedral complex, composed of `Co^(3+)` ion (central metal), two en molecules, two `CI^(-)` ions and `NO_(2)` ion, is

Options

A. 3
B. 4
C. 6
D. 5

Answer

C

Explanation

CN of `Co^(3+)` ion is 6. There are three structural isomers of the given complex:
`[CoC1_(2)(en_(2))]NO_(2), [CoC1(en)_(2)(NO_(2))]C1`
`[CoC1(en)_(2) (ONO)] C1`
Ethylenediamine always spans adjacent corner of an octahedron but the `C1^(-)` ligands (or `C1^(-)` and `NO_(2)//ONO)` can be on either adjacent or opposite corners. Therefore, there are two diastereomers, cis and trans of each of these. Because the trans isomer of each has several symmetry planes - one cut through the Co and the en ligands - it is achiral and has no enantiomers. However, the cis isomer of each is chiral and exist as a pair of enantiomers that are nonidentical mirror images.