Weak Field Ligand
Definition and meaning of Weak Field Ligand in chemistry.
A weak field ligand is a molecule or ion that produces a relatively small splitting of the d-orbital energy levels when it coordinates to a central transition metal ion. In crystal field theory, this small energy gap often results in high-spin complexes because electrons can easily occupy the higher-energy d-orbitals before pairing up.
In more detail
Ligands are arranged in the spectrochemical series based on the degree to which they split the d-orbitals of a metal center. Weak field ligands, such as halides and water, exert a weaker electrical field on the metal's d-electrons. Because the crystal field splitting energy is smaller than the spin-pairing energy, electrons will singly occupy all available d-orbitals before any pairing occurs. Consequently, complexes with weak field ligands tend to have a larger number of unpaired electrons, making them strongly paramagnetic and often brightly colored.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Crystal Field Splitting | Small |
| Typical Result | High-spin complex |
The fluoride ion (F-) is a classic weak field ligand; when it binds to a cobalt(III) ion to form the [CoF6]3- complex, it creates a high-spin complex with four unpaired electrons.
Frequently asked questions
What is an example of a weak field ligand?
Halide ions like chloride (Cl-) and fluoride (F-) are common weak field ligands found at the lower end of the spectrochemical series.