Arrange the following ligands in the increasing order of their field strength:
(A) $en$
(B) $edta^{4-}$
(C) $S^{2-}$
(D) $OH^-$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (C), (D), (B), (A)
Ligand field strength generally follows a pattern based on the donor atom. The strength typically increases in the following order: Halides < Oxygen donors < Nitrogen donors < Carbon donors
The field strength of ligands is determined using the spectrochemical series, which arranges ligands from weak field → strong field.
Weak field ligands → small crystal field splitting (Δ)
Strong field ligands → large crystal field splitting
Relevant order from the spectrochemical series: S²⁻ < OH⁻ < en < stronger ligands
(C) S²⁻
Sulphide ion is a very weak field ligand because it forms weaker crystal field splitting.
(D) OH⁻
Hydroxide is stronger than S²⁻ but still considered a weak field ligand.
(B) edta⁴⁻
EDTA is a hexadentate ligand and forms strong chelate complexes, producing larger crystal field splitting than OH⁻.
(A) en (ethylenediamine)
A strong field bidentate ligand placed higher in the spectrochemical series than the above ligands.
Increasing order of field strength
S²⁻ < OH⁻ < edta⁴⁻ < en
The correct answer is Option (1) → (C), (D), (B), (A).