Question

In potassium ferrocyanide, there are ____ pairs of electrons in the \(t_{2g}\) set of orbitals.

Hint:

Strong field ligands like CN⁻ cause maximum pairing of electrons in the lower energy t₂g orbitals, resulting in low-spin configurations in octahedral complexes.

Answer 1

Correct Answer: 3

To determine the number of electron pairs in the \(t_{2g}\) set of orbitals in potassium ferrocyanide, consider the electronic structure of the [\text{Fe(CN)}_6]^{4-} complex ion. In this complex, the iron (Fe) is in the +2 oxidation state, indicated by \text{Fe}^{2+}. Iron in the +2 state has an electron configuration of [Ar] 3d^6. When forming the octahedral complex, the d electrons are distributed among the t_{2g} and e_g\) orbitals.

Ligands like cyanide (CN⁻) create a strong field, causing a large splitting of the d orbitals into t_{2g}\) (lower energy) and e_g\) (higher energy) sets. Given the strong-field nature, electron pairing occurs in the t_{2g}\) set:

• There are 6 electrons in 3d\), which under the influence of the strong field, enter the lower energy t_{2g}\) orbitals completely.

Thus, we populate the t_{2g}\) orbitals with 6 electrons as follows: t_{2g} \rightarrow\) (↓, ↓, ↓).

Each pair of electrons (two) in an orbital constitutes a single electron pair, resulting in a total of 3 pairs in the t_{2g}\) orbitals. This result is verified given the specified range of 3,3.

Therefore, the complex contains 3 pairs of electrons in the t_{2g}\) orbitals.