Question

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

• A. $NO$
• B. $NH^{+}_{4}$
• C. $NH_{2}CH_{2}CH_{2}NH_{2}$
• D. $CO$

Answer 1

Answer: (B)

$NH^{+}_{4}$

Answer 2

Complexes are formed when ligands donate a pair of electrons to metals. In ammonia, $N$ atom has one lone pair of electrons. Nitrogen donates this lone pair of electrons to proton to form ammonium ion. So $N H _{4}^{+}$ ion does not have a lone pair of electrons which it can donate to central metal ion. Hence it cannot behave as a ligand.