Question

The most stable ion is
A.$Fe(OH)_{6}]^{3-}$
B.$Fe(Cl)_{6}]^{3-}$
C.$Fe(CN)_{6}]^{3-}$
D.$Fe(H_{2}O)_{6}]^{3+}$

Answer 1

Hint: To answer this question we must recall the general properties of complexes. The central metal atom is linked to ligands by donation of pairs of electrons by ligands to the central metal atom.

Complete answer:
- In coordination complexes, the cations with higher oxidation states result in the formation of more stable complexes with common ligands like ammonia or water.
- Moreover, with decrease in the size of the metal cation, the stability of these metal complexes increases.
- Stability of a coordination complex increases with an increase in charge density. More is the charge density on the metal ion, more strongly will the ligand be attached to the central metal ion and thus resulting in increased stability.
- The complex nature stability depends on the nature of the ligand as, the more easily the ligand can donate its electron pair, the greater is the stability of the complex. Thus, we can say that for higher stability of the complex, ligand should be more basic.
- Chelating the effect of ligands also increases the stability of metal ion complexes.
- Now for the question, we know that iron has an oxidation state of +3. And since cyanide has the highest stability, we can say that $Fe(CN)_{6}]^{3-}$ is the most stable ion.

The correct option is (C) .

Note:
Complex compounds are formed in several steps where each step is reversible. The stability of metal ion complexes varies due to various factors, namely the nature of ligands, charge on the metal ion and the size of metal ions.