Ligands and d-orbital Splitting

Study Notes

Strong-Field Ligands

Strong-field ligands create a larger crystal field splitting.
Examples include CN⁻, CO, and NO.
They lead to low-spin configurations in transition metal complexes.

Octahedral Splitting Diagram for [Fe(NO2)6]³⁻

Iron in [Fe(NO2)6]³⁻ has a +3 oxidation state, resulting in 5 d-electrons.
In an octahedral field, the d-orbitals split into two sets: t₂g (lower energy) and e₄g (higher energy).
For 5 d-electrons, the distribution follows: ↑↓ ↑ ↑ (with three in t₂g and two in e₄g).

Low Spin Splitting and Pairing Energy

Low spin splitting occurs when the crystal field splitting energy (Δ) is greater than the pairing energy (P).
It favors electron pairing in the lower energy t₂g orbitals over occupying higher energy e₄g orbitals.
As a result, the complex becomes low-spin with more paired electrons.

Corrected Crystal Field Stabilization Energy (CFSE) for Cobalt (III) (d⁶)

For low-spin Co³⁺ (d⁶), the 6 d-electrons are distributed as: ↑↓ ↑↓ ↑ (all t₂g are filled, and e₄g has one unpaired).
The CFSE is calculated as:
- CFSE = (number of electrons in t₂g × -0.4Δ) + (number of electrons in e₄g × 0.6Δ)
- CFSE = (4 × -0.4Δ) + (2 × 0.6Δ) = -1.6Δ + 1.2Δ = -0.4Δ.

Formula for CFSE (Octahedral)

The formula for calculating CFSE in octahedral complexes is:
- CFSE = (n_t₂g × -0.4Δ) + (n_e₄g × 0.6Δ)
- Where n_t₂g and n_e₄g are the number of electrons in the t₂g and e₄g orbitals, respectively.

Description

Test your knowledge on the effect of ligands on d-orbital splitting. Learn about strong-field ligands like CN- and CO, and weak-field ligands like I- and Br-. Understand how different ligands influence the size of Δ in d-orbital splitting diagrams.