Example 5.4

Example . Linkage isomerism arises in a coordination compound containing ambidentate ligand. A simple example is provided by complexes containing the thiocyanate ligand, NCS – , which may bind through the nitrogen to give M–NCS or through sulphur to give M–SCN. Jørgensen discovered such behaviour in the complex [Co(NH ) (NO )]Cl , which is obtained as the red form, in which the nitrite ligand is bound through oxygen (–ONO), and as the yellow form, in which the nitrite ligand is bound through nitrogen (–NO ). This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. An example is provided by [Co(NH ) ][Cr(CN) ], in which the NH ligands are bound to Co + and the CN – ligands to Cr + . In its coordination isomer [Cr(NH ) ][Co(CN) ], the NH ligands are bound to Cr + and the CN – ligands to Co + . 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(NH ) (SO )]Br and [Co(NH ) Br]SO . . . Linkage Isomerism . . Coordination Isomerism . . Ionisation Isomerism Out of the following two coordination entities which is chiral (optically active)? (a) cis -[CrCl (ox) ] (b) trans -[CrCl (ox) ] The two entities are represented as Draw structures of geometrical isomers of [Fe(NH ) (CN) ] Out of the two, (a) cis - [CrCl (ox) ] - is chiral (optically active).