Question

Discuss the nature of bonding in the following coordination entity on the basis of valence bond theory:

[FeF₆]³⁻

Explain the structure of [FeF₆]³⁻ on the basis of valence bond theory.

Answer 1

1. In this complex, the oxidation state of Fe is +3.
2. Orbitals of Fe⁺³ ion:
3. The complex ion [FeF₆]³⁻ is explained on the basis of valence bond theory as follows: Iron in this complex is in the +3 oxidation state, so the electronic configuration of Fe³⁺ is [Ar] 3d⁵. The fluoride ion (F⁻) is a weak field ligand and does not cause the pairing of electrons in the d-orbitals.
4. As a result, the five 3d electrons in Fe³⁺ remain unpaired. Since there are six ligands, the geometry of the complex is octahedral, requiring six hybrid orbitals.
5. Due to the weak field nature of F⁻, the complex uses outer d-orbitals (4d) for bonding, resulting in sp³d² hybridization.
6. The [FeF₆]³⁻ complex is an outer orbital octahedral complex. Because of the presence of five unpaired electrons, the complex is paramagnetic in nature.
7. The sp³d² hybridized orbitals of Fe are:
   

Hence, the geometry of the complex is found to be octahedral.