Question

(i) Write two postulates of Werner's coordination theory. 
(ii) Draw the geometrical isomers of [(NH_3)_3(NO_2)_3] and give their structures.

• A.
• B.
• C.
• D.

Hint:

Key Points: Werner explained coordination compounds using primary and secondary valencies. Octahedral complexes of type \(MA_3B_3\) show two geometrical isomers: fac (facial) and mer (meridional). fac → three identical ligands on one face; mer → arranged along a meridian.

Answer 1

The Correct Option is A

Concept:
Werner’s coordination theory explains the bonding and structure of coordination compounds. It distinguishes between ionizable and non-ionizable valencies and also explains the geometrical arrangement of ligands around the central metal ion. 

Step 1: Postulates of Werner’s Coordination Theory.
1. A metal atom or ion in a coordination compound exhibits two types of valencies: primary valency and secondary valency.
2. Primary valency corresponds to the oxidation state of the metal and is usually satisfied by negative ions. These are ionizable.
3. Secondary valency corresponds to the coordination number of the metal ion and is satisfied by neutral molecules or negative ions called ligands. These are non-ionizable and have a definite spatial arrangement. 

Step 2: Geometrical Isomers of MA3B3 Type Complex.
The complex [Co(NH₃)₃(NO₂)₃] is an octahedral complex of the type MA₃B₃.. It shows two geometrical isomers:

fac-isomer (facial):
The three identical ligands occupy adjacent positions at the corners of one triangular face of the octahedron.
fac-[Co(NH₃)₃(NO₂)₃] 

mer-isomer (Meridional):
The three identical ligands lie along a meridian of the octahedron, forming a plane that passes through the central metal atom.
mer-[Co(NH₃)₃(NO₂)₃] 

Thus, the complex exhibits two geometrical arrangements known as facial and meridional isomers.