Question

The stabilization of coordination compounds due to chelation is called the chelate effect. Which of the following is the most stable complex species?

• A. $\left[Fe\right(C_2{O}_4{)}_3{]}^{3-}$
• B. $\left[Fe\right(CO{)}_5]$
• C. $\left[Fe\right(CN{)}_6{]}^{3-}$
• D. $\left[Fe\right(H_{2}O{)}_6{]}^{3+}$

Answer 1

The correct option is A $\left[Fe\right(C_2{O}_4{)}_3{]}^{3-}$

Explaining the concept of chelation

It is the bonding between Metal ions and Ligands to form a cyclic complex. Chelation is the formation of two or more separate coordinate bonds between a single ligand and a central metal ion.

Most important is that the process of chelation stabilizes a coordination compound.

Stability of coordination compound through chelation :

Among the given coordination compounds only $\left[Fe\right(C_2{O}_4{)}_3{]}^{3-}$ is a coordination compound which is formed by the process of chelation, where the cyclization of the compound provides more stability than the other three coordination compounds.

In $\left[Fe\right(C_2{O}_4{)}_3{]}^{3-}$ , three oxalate ions $\left(C_2{O}_4^{2+}\right)$ are the bidentate ligands and acts as a chelating ligand and $F{e}^{3+}$ is the central metal ion. Two $O$ atoms from each $C_2{O}_4^{2-}$ forms the coordinate bond with central metal ion.

The structure of $\left[Fe\right(C_2{O}_4{)}_3{]}^{3-}$ is:


$CO,CN,H_{2}O$ are monodentate ligands so they can not act as chelating ligand.

Hence, the correct answer is option $c$.