[Fe(CN)₆]³⁻ should be an inner orbital complex. Ignoring the pairing energy, the value of crystal field stabilization energy for this complex is (-) ____________ Δ₀. (Nearest integer)

Solution

Chemistry ma’am · 3 steps

Inner orbital means low spin: put all five d electrons of Fe³⁺ into t_(2g), then count.

1. Find the d count. With six CN⁻ ligands and an overall charge of -3, iron is +3. Fe³⁺ is 3d⁵.
2. Low spin filling. An inner orbital complex uses d²sp³ hybridisation, which needs two empty 3d orbitals. So CN⁻, a strong field ligand, pairs the electrons, and all five go into t_(2g): the configuration is t_(2g)⁵ e_g⁰.

   CFSE = (-0.4 n_(t_(2g)) + 0.6 n_(e_g)) Δ₀ = (-0.4 × 5 + 0.6 × 0) Δ₀ = -2.0 Δ₀

3. So. Ignoring pairing energy, the CFSE is -2.0 Δ₀, so the blank is 2.

The common slip: 0. Filling d⁵ as high spin (t_(2g)³ e_g²) gives -1.2 + 1.2 = 0, not 2. CN⁻ is a strong field ligand, so the electrons pair up in t_(2g).

The idea to keep. Each t_(2g) electron is worth -0.4 Δ₀ and each e_g electron is worth +0.6 Δ₀. Decide high spin or low spin first, because the filling changes the answer.

Answer from the NTA final answer key. Solution by PrepWiser.