High Spin Complex
Definition and meaning of High Spin Complex in chemistry.
A high spin complex is a coordination compound in which the metal ion's d electrons occupy the maximum number of separate d orbitals rather than pairing up, because the ligand field splitting energy is smaller than the energy required to pair two electrons in one orbital.
In more detail
This arrangement follows Hund's rule and occurs with weak-field ligands (low on the spectrochemical series, such as halide ions or water), which produce a small crystal field splitting energy (Delta-o in an octahedral field). Because Delta-o is less than the pairing energy P, electrons fill the higher-energy eg orbitals singly before any pairing occurs in the lower-energy t2g set. High versus low spin only matters for octahedral d4 through d7 metal ions, since d1-d3 and d8-d10 configurations have just one possible arrangement. High spin complexes have more unpaired electrons and a larger magnetic moment than the corresponding low spin complex.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Applies to | Octahedral complexes with d4-d7 metal ions |
| Condition | Delta-o (crystal field splitting) < pairing energy P |
| Example ion | [Fe(H2O)6]2+ (t2g^4 eg^2, 4 unpaired electrons) |
The hexaaquairon(II) ion, [Fe(H2O)6]2+, is high spin: Fe2+ is d6, and water is a weak-field ligand, so the electron configuration is t2g^4 eg^2, giving four unpaired electrons and strong paramagnetism.
Frequently asked questions
What ligands favor high spin complexes?
Weak-field ligands low on the spectrochemical series, such as I-, Br-, Cl-, F-, OH-, and H2O, which produce a small Delta-o and favor filling all d orbitals singly before pairing.
How is high spin experimentally distinguished from low spin?
By magnetic susceptibility measurements: high spin complexes have more unpaired electrons and a larger measured magnetic moment than low spin complexes of the same metal and oxidation state.