Difference Between Bidentate and Ambidentate Ligands

Key Difference – Bidentate vs Ambidentate Ligands
 

The key difference between bidentate and ambidentate ligands is that bidentate ligands can bind to a central atom via two bonds at the same time whereas ambidentate ligands can form two bonds with a central atom, but form only one bond at a time.

Ligands are electron-rich molecules or anions that can donate lone electron pairs to an atom that has a positive electrical charge. There are several types of ligands named as Monodentate ligands, bidentate ligands, polydentate ligands, etc. based on the number of bonds they can form with an atom.

CONTENTS

1. Overview and Key Difference
2. What are Bidentate Ligands
3. What are Ambidentate Ligands
4. Similarities Between Bidentate and Ambidentate Ligands
5. Side by Side Comparison – Bidentate vs Ambidentate Ligands in Tabular Form
6. Summary

What are Bidentate Ligands?

Bidentate ligands are molecules or anions that can bind to an atom via two coordinate covalent bonds. Coordinate covalent bonds are a type of covalent bonds that are formed when an electron-rich chemical species donate lone electron pairs to an electron-deficient chemical species such as positively charged metal atoms. When ligands and cations bind in this way, a coordination compound is formed. The atom to which the ligands are bonded to is called the coordination center.

Figure 01: Ethylenediamine is a Bidentate Ligand

A bidentate ligand has two donor atoms. This means, there are two atoms that can donate their lone electron pairs. Some common examples for the bidentate ligands include oxalate ion (C₂O₄^2-) that has two oxygen atoms as donor atoms and ethylenediamine (C₂H₄(NH₂)₂) that has two nitrogen atoms as donor atoms.

What are Ambidentate Ligands?

Ambidentate ligands are molecules or ions that have two donor atoms but are capable of binding with an atom via only one donor atom at a time. Examples of ambidentate ligands include thiocyanate ion (SCN^–) in which both sulfur atom and a nitrogen atom are capable of donating lone electron pairs. But either the sulfur atom or nitrogen atom can bind to the coordination center at a time.

Figure 02: Thiocyanate is an Ambidentate Ligand

Another example is nitrate ion (NO₂^–) in which both nitrogen atom and oxygen atom can become a donor atom.

What are the Similarities Between Bidentate and Ambidentate Ligands?

• Both Bidentate and Ambidentate ligands have two donor atoms.
• Both ligands have at least two atoms with lone electron pairs.

What is the Difference Between Bidentate and Ambidentate Ligands?

Summary – Bidentate vs Ambidentate Ligands

Ligands are molecules or ions that can bind with electron-deficient atoms via coordinate covalent bonds. Bidentate ligands and ambidentate ligands are such two ligand forms. The difference between bidentate and ambidentate ligands is that bidentate ligands can bind with a central atom via two bonds at the same time whereas ambidentate ligands are capable of forming two bonds with a central atom but form only one bond at a time.

Reference:

1. “Ligands | Types of Ligands | Chelate Ligand, Denticity, Ambidentate Ligand | Chemistry | Byju’s.” Chemistry, Byjus Classes, 8 Mar. 2018. Available here  
2. Libretexts. “Ligands.” Chemistry LibreTexts, Libretexts, 19 Jan. 2018. Available here 

Image Courtesy:

1.’M-en1’By No machine-readable author provided (Public Domain) via Commons Wikimedia 
2.’PhSCN-PhNCS-comparison’ (Public Domain) via Commons Wikimedia  

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