# 5.8: Structural Isomers- Coordination Isomerism in Transition Metal Complexes


Coordination isomerism occurs in compounds containing complex anionic and cationic parts and can be viewed as the interchange of one or more ligands between the cationic complex ion and the anionic complex ion. For example, $$\ce{[Co(NH3)6][Cr(CN)6]}$$ is a coordination isomer with $$\ce{[Cr(NH3)6][Co(CN)6]}$$. Alternatively, coordination isomers may be formed by switching the metals between the two complex ions like $$\ce{[Zn(NH3)4][CuCl4]}$$ and $$\ce{[Cu(NH3)4][ZnCl4]}$$.

Exercise $$\PageIndex{1}$$

Are $$\ce{[Cu(NH3)4][PtCl4]}$$ and $$\ce{[Pt(NH3)4][CuCl4]}$$ coordination isomers?

Solution

Here, both the cation and anion are complex ions. In the first isomer, $$\ce{NH3}$$ is attached to the copper and the $$\ce{Cl^{-}}$$ are attached to the platinum. In the second isomer, they have swapped.

Yes, they are coordination isomers.

Exercise $$\PageIndex{2}$$

What is one coordination isomer of $$\ce{[Co(NH3)6] [Cr(C2O4)3]}$$?

Solution

Coordination isomers involve swapping the species from the inner coordination sphere to one metal (e.g, cation) to inner coordination sphere of a different metal (e.g., the anion) in the compound. One isomer is completely swapping the ligand sphere, e.g, $$\ce{[Co(C2O4)3] [Cr(NH3)6]}$$.

Alternative coordination isomers are $$\ce{ [Co(NH3)4(C2O4)] [Cr(NH3)2(C2O4)2]}$$ and $$\ce{ [Co(NH3)2(C2O4)2] [Cr(NH3)4(C2O4)]}$$.