Co-ligand isomers

In the case of certain mixed ligand complexes, the total elemental composition due to the co-ligands becomes the same. These type of ligand isomers are known as co-ligand isomers. 

Generally, a pair of co-ligand isomers results due to an intramolecular nucleophilic addition reaction in coordinated ligands. One of the isomers is an ordinary complex, while the other isomer formed upon the above-mentioned reaction is a chelate. 

An illustration of co-ligand isomerism [1] in ortahedral complexes is provided by a5-[Co(en)2(NH2CH2CN)Cl] which converts into its chelate form of the co-ligand isomer [Co(en)(NH2CH2C(NH2)=NCH2CH2NH2) Cl] in nearly neutral or basic solution, as shown in F pre 8. 

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