Question

Which one of the following is an ambidentate ligand? ________.

• A. Oxalate
• B. Carbon monoxide
• C. Ethylene diamine
• D. Ammonia
• E. Nitrite

Hint:

Ambidentate ligands lead to linkage isomerism in coordination compounds.

Answer 1

Answer: (E)

Step 1: Understanding the Concept
A ligand is a molecule or ion that can donate a pair of electrons to a central metal ion to form a coordinate bond. An ambidentate ligand is a specific type of monodentate ligand that possesses two or more different donor atoms, but coordinates to the metal ion through only one of them at a time in any given complex.
Step 2: Detailed Explanation
Let's examine the potential donor atoms in each option.
(A) Oxalate (\(C_2O_4^{2-}\)): The structure has two carboxylate groups, \([OOC-COO]^{2-}\). Each group has an oxygen atom that can donate electrons. It can use both donor atoms to bind to the same metal ion simultaneously, forming a ring. This makes it a bidentate chelating ligand, not an ambidentate ligand.
(B) Carbon monoxide (CO): It typically binds through the carbon atom's lone pair (\(M \leftarrow C \equiv O\)). It is a monodentate ligand with only one preferred donor site.
(C) Ethylene diamine (\(H_2N-CH_2-CH_2-NH_2\)): It has two nitrogen atoms, each with a lone pair. It can bind through both nitrogen atoms to the same metal ion simultaneously, making it a bidentate chelating ligand.
(D) Ammonia (\(NH_3\)): It has one nitrogen atom with a lone pair, making it a simple monodentate ligand.
(E) Nitrite (\(NO_2^-\)): The nitrite ion has a structure with two different potential donor atoms: the nitrogen atom and the oxygen atoms. It can form a coordinate bond in two different ways: - Through the nitrogen atom: \(M \leftarrow NO_2\) (This complex is called a "nitro" complex). - Through an oxygen atom: \(M \leftarrow ONO\) (This complex is called a "nitrito" complex). Since it is a single ligand that can bind through two different atoms (but only one at a time), it is a classic example of an ambidentate ligand. Other examples include thiocyanate (\(SCN^-\)), which can bind via S or N.
Step 4: Final Answer
The nitrite ion is an ambidentate ligand.