What is the spectrochemical series?

The spectrochemical series is a list of ligands arranged according to the strength of the crystal field they produce in a transition metal complex.

Here’s a simple explanation:

1. Purpose:
   • It helps predict whether a complex will be high-spin or low-spin.
   • Strong-field ligands cause a large splitting of the d-orbitals → low-spin.
   • Weak-field ligands cause a small splitting → high-spin.
2. Order of ligands (simplified):
   • Weak-field ligands: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O
   • Intermediate: NH₃
   • Strong-field ligands: CN⁻, CO
3. Key point:
   • Ligands on the left of the series produce small splitting (high-spin complexes).
   • Ligands on the right produce large splitting (low-spin complexes).

In short: The spectrochemical series is a ranking of ligands from weak to strong based on how much they split the d-orbitals in a transition metal complex.