Advanced Topic 208 of 1102 Bonding & Molecular Structure
Spectrochemical Series
An ordering of ligands by the crystal-field splitting they cause.
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In-depth explanation of Spectrochemical Series
The spectrochemical series ranks ligands in order of the crystal field splitting they produce, from weak field to strong field. A typical order is I- less than Br- less than Cl- less than F- less than OH- less than H2O less than NH3 less than en less than CN- less than CO. Stronger field ligands produce a larger splitting delta_o, which affects the colour absorbed and whether electrons pair in the lower orbitals. The series is an empirical ordering derived from spectroscopic data and is broadly the same across many metals. It is a practical tool for predicting complex properties.
Going deeper: Spectrochemical Series
Key ideas: Memorize weak to strong: I- below Br- below Cl- below F- below OH- below H2O below NH3 below en below NO2- below CN- below CO. Also metal effects: delta_o rises with oxidation state (Fe3+ above Fe2+) and down a group (3d below 4d below 5d, about 30 to 50 percent each). Pairing is more likely for 4d and 5d metals.
Common mistakes and connections: Common mistakes include mixing the order of NH3 and H2O, or thinking that charge on the ligand determines the field strength (the OH- is weaker than NH3, and CO neutral is the strongest). Another is assuming 3d complexes with F- are low spin. Links to CFT, colour changes, magnetic properties and pi acceptor ligands.
Visualization of Spectrochemical Series
Ligands ordered from weak to strong field, I- to CO. Stronger field ligands cause a larger d-orbital splitting. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Cyanide is a strong field ligand that produces a large splitting, while chloride is a weak field ligand that produces a small splitting.
Frequently asked questions about Spectrochemical Series
What is Spectrochemical Series?
An ordering of ligands by the crystal-field splitting they cause.
Is Spectrochemical Series a beginner, intermediate or advanced topic?
Spectrochemical Series is a advanced topic in Bonding & Molecular Structure. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Spectrochemical Series?
Study these earlier topics in Bonding & Molecular Structure first: Coordination Number, Chelation, Crystal Field Theory.
What comes after Spectrochemical Series?
The next topics in Bonding & Molecular Structure are High Spin and Low Spin Complexes and Color of Transition Metal Complexes.
Can I practise Spectrochemical Series with quizzes?
Yes. The interactive lesson includes a self-check question on Spectrochemical Series, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Spectrochemical Series fits in Bonding & Molecular Structure
Spectrochemical Series is topic 93 of 104 in Bonding & Molecular Structure.