Question

Which one of the following will not show geometrical isomerism
A \[\left[ Cr{{\left( N{{H}_{3}} \right)}_{4}}C{{l}_{2}} \right]Cl\]
B \[\left[ Co{{\left( en \right)}_{2}}{{\left( Cl \right)}_{2}} \right]Cl\]
C \[\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}N{{O}_{2}} \right]C{{l}_{2}}\]
D \[\left[ Pt{{\left( N{{H}_{3}} \right)}_{2}}C{{l}_{2}} \right]\]

Answer 1

Hint: Geometrical isomerism is a stereoisomerism in complex compounds in which isomers are those compounds whose molecular formula is the same but the arrangement of ligands are of two types (adjacent and opposite). Also, we can say that if a compound has two different types of ligands and those ligands can be arranged adjacent (cis isomers) and opposite (trans) to each other so both compounds are geometrical isomers of each other.

Complete Step by Step Answer:
In the first compound, \[\left[ Cr{{\left( N{{H}_{3}} \right)}_{4}}C{{l}_{2}} \right]Cl\] four ammonia and two chlorine ligands are present such as\[\left[ M{{\left( A \right)}_{4}}{{\left( B \right)}_{2}} \right]\].

Now in one case, both B ligands can be on the same side each other and in another arrangement, they occupy opposite positions (simultaneously ligand A) such as AA, BB, and AB, AB. Thus it will show geometrical isomerism.

Similarly compound second, \[\left[ Co{{\left( en \right)}_{2}}{{\left( Cl \right)}_{2}} \right]Cl\] also contains two types of ligands such as \[\left[ M{{\left( A \right)}_{2}}{{\left( B \right)}_{2}} \right]\] where A is en and B is Cl. Now, these also can be arranged adjacent and opposite in complex spaces giving geometrical isomerism phenomenon. In option fourth, the compound is again of \[\left[ M{{\left( A \right)}_{2}}{{\left( B \right)}_{2}} \right]\] type so it will also show geometrical isomerism.

In compound third, \[\left[ Co{{\left( N{{H}_{3}} \right)}_{5}}N{{O}_{2}} \right]C{{l}_{2}}\] there are five ammonia and one chlorine such as \[\left[ M{{\left( A \right)}_{5}}{{\left( B \right)}_{1}} \right]\]so it can only form only one arrangement AA and AB. As A ligand is adjacent and opposite to each other but ligand B has no other arrangement as compared to ligand A so it cannot form geometrical isomers.
Thus, the correct option C.

Note: The geometrical isomerism is found in heteroleptic compounds (which means a different type of ligands or minimum two A and two B type of ligands needed for geometrical isomerism) because of different geometrical arrangements in the complex sphere. When two same ligands are placed at the adjacent position then it is said to be a cis isomer otherwise (if at the opposite position) said to be a trans isomer. In this ligands are arranged at the different position as position within the complex sphere.