Among the following coordination compounds, the complexes which can s…

The correct answer is Option (2) → B and C only

Linkage isomerism arises when a complex contains an ambidentate ligand, a ligand that can bind to the metal through two different donor atoms. The common examples are:

    \( \ce{NO2^{-}} \): through N (nitrito-N) or through O (nitrito-O)
    \( \ce{SCN^{-}} \): through S (thiocyanato-S) or through N (thiocyanato-N)

The ambidentate ligand must be inside the coordination sphere (inside the square bracket). An ambidentate ion present only as a counter ion is not bonded to the metal, so it cannot give linkage isomers.

• (A) \( \ce{[Co(NH3)5(CH3COO)](NO2)2} \) — Incorrect. The \( \ce{NO2^{-}} \) ions are outside the bracket, and the ligands \( \ce{NH3} \) and \( \ce{CH3COO^{-}} \) each bind through one kind of atom only (N and O).

• (B) \( \ce{[Co(H2O)5(SCN)]Br2} \) — Correct. The SCN⁻ ligand is coordinated and can bind through S or through N.

• (C) \( \ce{[Co(CH3NH2)5(NO2)]Br2} \) — Correct. The NO₂⁻ ligand is coordinated and can bind through N or through O.

• (D) \( \ce{[Co(CH3NH2)5(Br)](SCN)2} \) — Incorrect. The \( \ce{SCN^{-}} \) ions are counter ions outside the bracket, so no linkage isomer is possible.

NCERT (2026-27 edition):
Linkage Isomerism