The complex [Co(NH_3)_4(NO_2)_2]Cl exhibits Coordination isomerism Li…

The correct answer is Option (1) → B, D and E only

Each type of structural or stereoisomerism needs a particular feature in the complex. In \( \ce{[Co(NH3)4(NO2)2]Cl} \) the coordination sphere holds four \( \ce{NH3} \) and two NO₂^– around \( \ce{Co^{3+}} \) (octahedral), and Cl^– is the counter ion.

• (A) Coordination isomerism — False. It needs both the cation and the anion to be complex ions, so that ligands can be exchanged between two metal centres. Here the anion is a simple Cl^–.

• (B) Linkage isomerism — True. NO₂^– is an ambidentate ligand; it can bind through N (nitrito-N) or through O (nitrito-O, –ONO).

• (C) Solvate isomerism — False. It needs a solvent molecule, usually water, that can be inside or outside the coordination sphere (as in \( \ce{[Cr(H2O)6]Cl3} \)). This complex has no water.

• (D) Ionisation isomerism — True. The counter ion Cl^– can itself act as a ligand and change place with an NO₂^–, giving \( \ce{[Co(NH3)4(NO2)Cl]NO2} \).

• (E) Geometrical isomerism — True. An octahedral complex of the type [MA₄B₂] has cis and trans forms: the two NO₂^– can be adjacent or opposite.

NCERT (2026-27 edition):
Linkage Isomerism

Ionisation Isomerism – “This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion. An example is provided by the ionisation isomers [Co(NH₃)₅(SO₄)]Br and [Co(NH₃)₅Br]SO₄.”

Geometric Isomerism – “This type of isomerism arises in heteroleptic complexes due to different possible geometric arrangements of the ligands. … Such isomerism is not possible for a tetrahedral geometry but similar behaviour is possible in octahedral complexes of formula [MX₂L₄] in which the two ligands X may be oriented cis or trans to each other (Fig. 5.3).”