Valence Bond Theory - Chemical Bonding, Inorganic Chemistry

The valence bond theory is a model used to explain chemical bonding in inorganic compounds, such as coordination complexes. It describes the formation of chemical bonds in terms of overlapping atomic orbitals. In the case of [Fe(CN)6]2-, the hybridization of the central iron atom will be discussed.

Hybridization of [Fe(CN)6]2-
The coordination complex [Fe(CN)6]2- consists of a central iron (Fe) atom surrounded by six cyanide (CN-) ligands. To determine the hybridization of the central atom, we need to consider the electronic configuration and bonding pattern.

Electronic Configuration of Fe
Iron (Fe) has an atomic number of 26, with the electronic configuration [Ar] 3d6 4s2. In the ground state, the outermost 4s and 3d orbitals are available for bonding.

Bonding in [Fe(CN)6]2-
Each cyanide ligand (CN-) has a carbon atom bonded to a nitrogen atom. The carbon atom uses sp hybrid orbitals for bonding, while the nitrogen atom uses its lone pair in a p orbital. The bonding between the central iron atom and the cyanide ligands occurs through the donation of the lone pairs of nitrogen to the empty d orbitals of iron.

Hybridization of Fe
The central iron atom in [Fe(CN)6]2- undergoes hybridization to form bonding orbitals. In this case, the hybridization can be explained as follows:

1. Promotion: One electron from the 4s orbital is excited to the empty 3d orbital, resulting in the electronic configuration [Ar] 3d7 4s1.

2. Hybridization: The excited iron atom undergoes sp3d2 hybridization, involving five orbitals. This hybridization results in the formation of six bonding orbitals, which can accommodate the six ligands.

3. Bonding: The sp3d2 hybrid orbitals of iron overlap with the nitrogen orbitals of the cyanide ligands, forming sigma bonds. The bonding occurs through the donation of the lone pairs of nitrogen to the empty d orbitals of iron.

Conclusion
In summary, the valence bond theory can be used to explain the hybridization of the central iron atom in [Fe(CN)6]2-. Through promotion and hybridization, the iron atom forms six sigma bonds with the cyanide ligands, resulting in an octahedral coordination geometry.