Which one of the following is an ambidentate ligand?

Solution & Explanation

\textbf{Answer:} (C) Thiocyanate. \textbf{Solution:} An ambidentate ligand has two different donor atoms but coordinates through only one of them at a time, so it can bind to the metal through either site. The thiocyanate ion, $\mathrm{SCN}{}^{-}$, can coordinate either through sulfur ($\mathrm{M}-\mathrm{SCN}$, thiocyanato-S) or through nitrogen ($\mathrm{M}-\mathrm{NCS}$, thiocyanato-N / isothiocyanato). Having two distinct possible donor atoms makes it ambidentate (and gives rise to linkage isomerism). The distractors differ in denticity, not ambidentacy: ethane-1,2-diamine (en) and oxalate $\mathrm{C}{}_2\mathrm{O}{}_4{}^{2-}$ are bidentate, and $\mathrm{EDTA}{}^{4-}$ is hexadentate — each binds through a fixed set of donor atoms simultaneously. Hence the ambidentate ligand is thiocyanate, option (C).