Ligands are chemical species that attach to a central metal atom or ion within a complex. The strength of a ligand is quantified by its capacity to provide electron pairs to the metal center. Ligands are categorized as strong or weak field based on their influence on the splitting of the metal ion's d-orbitals.
- \( \text{F}^- \) (Fluoride ion): \( \text{F}^- \) functions as a weak field ligand. As a halide ion, its capability to split the metal ion's d-orbitals is limited.
- EDTA (Ethylenediaminetetraacetate): EDTA is classified as a strong field ligand. Its nature as a chelating ligand, involving attachment to the metal center via multiple donor atoms, confers significant ligand strength.
- en (Ethylenediamine): en is a bidentate ligand, capable of donating two lone pairs to the metal. It is also considered a strong field ligand, though its strength is less than that of EDTA.
- CO (Carbon monoxide): CO is identified as a very strong field ligand. It forms robust bonds with the metal center through its lone pair, and is recognized for its role in generating highly stable metal complexes.
Step 1: Conclusion
Given that fluoride (\( \text{F}^- \)) exhibits the lowest capacity among the provided ligands to split the metal's d-orbitals, the correct selection is \( \boxed{\text{F}^-} \).