Question

Which of the following species is not expected to be a ligand?

• A. $CO$
• B. $N{H}_4^{+}$
• C. $NO$
• D. $N{H}_{2}C{H}_{2}C{H}_{2}N{H}_2$

Answer 1

The correct option is B $N{H}_4^{+}$

Definition of Ligand

In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom/ion by donating a pair of electrons to form a coordination complex.

Analyzing the options

Option(a)

In $NO$ (Nitrosyl), $N$ atom has one lone pair of electrons. Nitrogen donates this lone pair to central atom during the formation of complexes, and thus acts as a ligand.



Option (b)

$N{H}_4^{+}$ ion does not have a lone pair of electrons and thus cannot participate in complex formation; therefore, it is not a ligand.

Option (c)

$N{H}_{2}C{H}_{2}C{H}_{2}N{H}_2$ is a bidentate ligand or chelating ligand as it has more than one donor atom. In ethylenediamine(en), each $N$ is a donor atom and thus, ethylenediamine act as a ligand.


Option (d)

$Co$ is a ligand that can donate a pair of electrons to central metal ion for complex formation and thus acts as a ligand.

Thus, from the above analysis it is concluded that option (b), i.e., $N{H}_4^{+}$ species is not expected to be a ligand.

Hence, the correct answer is option (b).