Question

Explain the structure of K₃[Fe(CN)₆] on the basis of valence bond theory.

Answer 1

Electronic configuration of Fe = [Ar] 4s² 3d⁶

1. The structure of K₃[Fe(CN)₆] is explained using Valence Bond Theory (VBT).
2. The central metal ion in the complex is Fe³⁺.
3. The atomic number of iron is 26, so its electronic configuration is [Ar] 3d⁶ 4s².
4. In the +3 oxidation state, Fe³⁺ has the configuration 3d⁵, after losing two 4s electrons and one 3d electron.
5. The complex contains six cyanide ions (CN⁻) as ligands.
6. CN⁻ is a strong field ligand and causes pairing of electrons in the 3d orbitals of Fe³⁺.
7. This electron pairing leaves two empty 3d orbitals available for bonding.
8. One 4s orbital and three 4p orbitals also participate in bonding.
9. These orbitals hybridize to form d²sp³ hybrid orbitals.
10. Six sigma bonds are formed by the overlap of these hybrid orbitals with lone pairs from six CN⁻ ligands.
11. The resulting geometry of the complex ion [Fe(CN)₆]³⁻ is octahedral.
12. Since all electrons are paired, the complex is diamagnetic.

Therefore, K₃[Fe(CN)₆] is an example of an inner orbital, low-spin, octahedral complex.