Question

Find the number of geometrical isomers in $[Co(en)(pn){(N{O_2})_2}]$ .
(a) $5$
(b) $3$
(c) $6$
(d) $4$

Answer 1

Hint: First we have to know what are the different types of geometrical isomers of any coordination compound. Then draw the structure, by viewing the structure we can easily know about the structure that will help to find the geometrical isomers.

Complete answer:
Starting from the definition of Geometrical isomerism:
Geometrical isomerism: The isomerism in which the coordination compounds have the same molecular formula, same functional groups but the spatial arrangement of some compounds are different given in the figure below.

                                                     $ \rightleftharpoons $
There are the types of geometrical isomers:
(a) cis and trans isomers.
(b) facial and meridional isomers.
This compound has four geometrical isomers.
Two cis- and trans- , two mer- and fac- and one coordination isomer. But, there are only four geometrical isomers.

Hence, the correct option is (d) $4$ .

Additional information:
There are different types of isomers in the coordination compounds:
(a) Stereoisomers: The molecules having the same chemical formulas and bonds but their spatial arrangement of the atoms are different are called stereoisomers.
(b) Structural isomers: The molecules which have the same chemical formula but the structure is not same, i.e, the arrangement of atoms are not same are called Structural isomers.
(a) Stereoisomers
Types of stereoisomers are:
(a) Geometrical isomers
(b) Optical isomers
(b) Structural isomers
Types of Structural isomers are:
(a) Linkage Isomerism
(b) Coordination Isomerism
(c) Ionization Isomerism
(d) Solvate Isomerism

Note:
Enantiomers and Diastereomers are the types of the stereoisomers, where the enantiomers are the stereoisomers having non-superimposable mirror image of each other whereas the diastereomers are the stereoisomers having non-superimposable mirror image of each other with two or more stereo centres.