ChemWhiz ReferenceCoordination Chemistry
Spectrochemical Series and Spin States
A general-chemistry reference for comparing ligand field strength and deciding when octahedral complexes can be high spin or low spin.
01Use this when
Deciding high-spin vs low-spin for an octahedral complex and comparing ligand field strength.
02Conditions
Runs from weak-field (small Δ) to strong-field (large Δ) for otherwise comparable complexes.
03Watch out
Strong-field / large Δ favors low spin; the metal, its charge, and geometry also shift Δ.
Ligand Field Strength (Weak to Strong)
Compare Δoct with the pairing energy P: Δoct < P gives high spin, Δoct > P gives low spin.
| 1 | I- | iodide | weaker end |
| 2 | Br- | bromide | increasing Δoct → |
| 3 | Cl- | chloride | increasing Δoct → |
| 4 | F- | fluoride | increasing Δoct → |
| 5 | OH- | hydroxide | increasing Δoct → |
| 6 | C2O42- | oxalate (bidentate) | increasing Δoct → |
| 7 | H2O | aqua | increasing Δoct → |
| 8 | NH3 | ammine | increasing Δoct → |
| 9 | en | ethylenediamine | increasing Δoct → |
| 10 | NO2- | nitro (N-bound nitrite) | increasing Δoct → |
| 11 | CN- | cyanide | stronger end |
Important Notes
- The order runs from smaller to larger crystal-field splitting for otherwise comparable complexes. It is qualitative, not a universal numerical scale.
- For octahedral d4, d5, d6, and d7 complexes, compare Δoct with the electron-pairing energy P: Δoct < P gives high spin; Δoct > P gives low spin.
- Metal identity, oxidation state, 3d/4d/5d row, geometry, and the full ligand environment all affect Δ. A ligand name alone is not a complete spin-state calculation.
- For a mixed-ligand complex, there is no strongest-ligand-wins rule. Use a supplied Δoct/P comparison or experimental spin information. If neither is available and the d count is spin-sensitive, the spin state may be underdetermined.
- For octahedral d0 to d3 and d8 to d10 configurations, field strength does not create two alternative high-spin and low-spin fillings.
- Tetrahedral complexes are ordinarily treated as high spin in general chemistry because Δtet is small. Square-planar d8 complexes use a different splitting pattern and should be analyzed separately.
Verification references: Ligand ordering based on OpenStax Chemistry 2e, Section 19.3 (Spectroscopic and Magnetic Properties of Coordination Compounds), extended with OH- and oxalate per the standard spectrochemical series..