Linkage Isomerism arises in coordination compounds containing ambidentate ligands.

• An ambidentate ligand is one that can coordinate to the central metal through two different atoms.
• The $N{O}_2^{-}$ ion can coordinate either through the nitrogen atom ($M-N{O}_2^{\text{, nitro}}$) or through the oxygen atom ($M-ON{O}^{\text{, nitrito}}$).
• Since these two complexes differ only in the atom through which the nitrite ligand is linked to the Cobalt, they are linkage isomers.