The spectrochemical series is a list of ligands arranged in order of their ability to split the d-orbital energies of a transition metal ion in a coordination complex. In simpler terms, it ranks ligands from weak field (which cause small splitting of d-orbitals) to strong field (which cause large splitting).
Key Points:
- Purpose:
- Helps predict whether a complex will be high-spin or low-spin.
- Helps explain color, magnetic properties, and stability of complexes.
- Weak Field Ligands:
- Cause small splitting of the metal’s d-orbitals.
- Usually result in high-spin complexes (more unpaired electrons).
- Examples: iodide, bromide, chloride, fluoride, hydroxide, water.
- Strong Field Ligands:
- Cause large splitting of d-orbitals.
- Usually result in low-spin complexes (fewer unpaired electrons).
- Examples: ammonia, ethylenediamine, cyanide, carbon monoxide.
- Order:
- The ligands are arranged from weakest to strongest field.
- This order is called the spectrochemical series.
- Applications:
- Predict magnetic behavior (high-spin or low-spin).
- Predict color of complexes (because d-orbital splitting affects absorption of light).
- Helps understand reactivity and stability of coordination compounds.