Question

Which is the strongest ligand?

• A. Fluoride ion $\left(F^{-}\right)$
• B. Chloride ion $\left(C{l}^{-}\right)$
• C. Cyanide ion $\left({\mathrm{CN}}^{-}\right)$
• D. Bromide Ion $\left({\mathrm{Br}}^{-}\right)$

Answer 1

The correct option is C

Cyanide ion $\left({\mathrm{CN}}^{-}\right)$

Ligands:

• Ligands are ions or molecules that are bound to the coordination entity's central atom/ion.

Option (C)

• ${\mathrm{CN}}^{-}$ is a strong field ligand because of the highest value of $∆$among the given ligands. It is classified as a pseudohalide ion. Pseudohalide ions are more powerful coordinating ligands with the ability to form $\sigma$ relationship and $\pi$ bond .
• A ligand spectrochemical series in which the ligands are arranged in increasing order of field strength:

${\mathrm{I}}^{-}<{\mathrm{Br}}^{-}<{\mathrm{SCN}}^{-}<{\mathrm{Cl}}^{-}<{\mathrm{S}}^{2-}<{\mathrm{F}}^{-}<{\mathrm{OH}}^{-}<{\mathrm{C}}_2{{\mathrm{O}}_4}^{2-}<{\mathrm{H}}_2\mathrm{O}<{\mathrm{NCS}}^{-}<{\mathrm{edta}}^{4-}<{\mathrm{NH}}_3<\mathrm{en}<{\mathrm{CN}}^{-}<\mathrm{CO}$.

Therefore, Option (C) is the correct answer.