Which of the following ligands is considered a stronger field ligand?

Cyanide is considered a stronger field ligand due to its ability to create a more significant crystal field splitting within coordination complexes. In crystal field theory, ligands can be classified based on their strength, which influences the splitting of d-orbitals in transition metal complexes. Strong field ligands, like cyanide, cause a large energy difference between the lower and upper sets of d-orbitals, leading to a situation where electrons pair up in the lower energy d-orbitals rather than occupying the higher energy ones.

This strong splitting is associated with ligands that have high electronegativity and effective π-acceptor ability, which is characteristic of cyanide. The presence of a negative charge on the cyanide ion and its ability to form strong covalent bonds with metal centers further contribute to its strength as a ligand. Consequently, this property makes cyanide suitable for forming stable low-spin complexes, commonly discussed in coordination chemistry.

In contrast, ligands like iodide, fluoride, and chloride are classified as weaker field ligands and do not create as significant a splitting effect on the d-orbitals when bonded to transition metals. This results in different electronic configurations within metal complexes, leading to distinct chemical and physical properties.