Question

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

Answer 1

1. The complex K₃[Fe(CN)₆] consists of Fe³⁺ as the central metal ion.
2. According to Valence Bond Theory (VBT), the Fe³⁺ ion undergoes d²sp³ hybridization.
3. This means Fe³⁺ mixes two of its 3d orbitals, one 4s orbital, and three 4p orbitals to form six hybrid orbitals.
4. These six hybrid orbitals are directed towards the six positions around the central Fe³⁺ ion and form bonds with the six cyanide (CN⁻) ligands.
5. The six hybrid orbitals formed by d²sp³ hybridization arrange themselves in an octahedral geometry to minimize electron repulsions between the ligands.
6. Therefore, the six cyanide ions are arranged at the vertices of an octahedron, with the central Fe³⁺ ion at the center.
7. Each CN⁻ ligand coordinates to Fe³⁺ by donating a lone pair of electrons from its carbon atom to one of the hybrid orbitals of Fe³⁺.
8. The geometry of K₃[Fe(CN)₆] is octahedral based on the d²sp³ hybridization of Fe³⁺.