Ligand Important Terms

Some of the important terms related to ligands are discussed below:

• Chelate Effect
• Ambidentate Ligands
• Bridging Ligands
• Coordinate Compounds
• Coordination Number
• Denticity

Chelate Effect

Chelate effect attributes to the property of polydentate ligands which allows them more efficient bonding with the central atom as there is more than one donor site in these ligands as compared to monodentate ligands which have only one donor site for bond formation. Thus, these ligands are also known as chelating ligands and the coordinate compound formed is known as the chelate.

In other words, it can be said that the effect which explains the improved affinity of chelating ligands towards the central atom than monodentate ligands is known as the chelate effect.

Ambidentate Ligands

Ambidentate ligands are those ligands which have more than one potential donor site for bond formation but at a particular time, only one of them takes part in bond formation. The choice of the donor site depends on some certain external factors.

For example, SCN^– is an ambidentate ligand which has two donor sites a Nitrogen atom and a Sulphur atom, but only one of them takes part in bond formation at a particular time.

Bridging Ligands

Bridging Ligands are the ligands in which the donor atom makes coordinate bond with more than two other atoms. These are called so as structure of the coordination compound formed by them is similar to a bridge with the metal atoms at end and the ligand in between them. The donor atom in bridging ligands has at least two lone pairs. Some examples of bridging ligands are OH⁻, S₂⁻, NH₂⁻, CO, etc.

Coordinate Compounds

Coordinate compounds are a class of chemical compounds in which a central metal atom or ion is linked to surrounding molecules through a coordinate bond. A coordinate bond is formed by the complete transfer of electrons from the donor atom to the central atom. Central metal atom is also called as Lewis acid and the donor element is called as Lewis base. The donor element is termed as the ‘Ligand’.

An example of coordinate compounds is [Fe(CN)₆]^4-. Here, Fe is the central metal atom and CN^– is the ligand.

Denticity

Denticity is the number of donor groups in a ligand that binds to a central metal atom in a coordination complex. It determines the bonding of a Ligand. Denticity of a ligand can be determined by its coordination number.

Coordination Number

The total number of donor atoms (Ligands) attached to the central metal atom is known as its coordination number. It is also known as ligancy.

Ligands are ions or molecules that form a bond with the central atom of a coordination compound by donating its pair of electrons to it. A ligand may be positively charged, negatively charged, or neutral. Ligands act as electron-donating species and can be called Lewis bases whereas the central atom acts as an electron pair acceptor and hence be called a Lewis Acid.

In this article, we will discuss the definition of a ligand, various types of ligands, and their examples.