Question

Which of the following complexes show linkage isomerism?

(i) \[\ce{[Co(NH3)5 (NO2)]^{2+}}\]

(ii) \[\ce{Co(H2O)5 CO]^{3+}}\]

(iii) \[\ce{[Cr(NH3)5 SCN]^{2+}}\]

(iv) \[\ce{Fe(en)2 Cl2]^+}\]

Answer 1

(i) \[\ce{[Co(NH3)5 (NO2)]^{2+}}\]

(iii) \[\ce{[Cr(NH3)5 SCN]^{2+}}\]

Explanation:

In the given complexes at \[\ce{[Co(NH3)5 (NO2)]^{2+}}\] and \[\ce{[Cr(NH3)5 SCN]^{2+}}\] the central metal atom (i.e. Co and Cr respectively) are bonded with ligands \[\ce{NO2}\] and \[\ce{SCN}\] separately. These ligands are ambidentate ligands and can link themselves with the central atom in two different ways exhibiting linkage isomerism (as mentioned below) -

In \[\ce{NO2}\] linkage isomerism arises in a coordination compound containing ambidentate ligand. A simple example is provided by complexes containing the thiocyanate ligands. \[\ce{NCS^-}\], which may bind through the nitrogen to give \[\ce{M-NCS}\] or through sulpur to give \[\ce{M-SCN}\].

In \[\ce{NO2}\] such behaviour in the complex \[\ce{[Co(NH3)5NO2]^{+2}}\], obtained in the red form, when nitrite ligand is bound through oxygen \[\ce{(ONO)}\], and in yellow form, when the nitrite ligand is bound through nitrogen (^–NO₂)