Chelate Ligand

A coordination or complex compound is one in which two or more anions or neutral molecules are coordinated to a metal atom or ion. In most cases, a coordination compound contains one or more complex ions. For example, K₄[Fe(CN)₆] is made up of a complex ion, [Fe(CN)₆]⁴⁺. 

A ligand is a chemical or ionic species that becomes directly linked to the central metal atom or ion during complex formation. Coordinate bonds connect the ligands to the central atom or ion. As a result, ligands are referred to as the coordinating group, molecule, or ion in a complex ion. A chelate is a molecule that consists of a central metal atom that is linked to a ligand that has at least two or more donor sites. The creation of a cyclic configuration around the core metal atom is caused by di- and polydentate ligands. Such a cyclic metal complex is known as a chelate, and the ligands that produce chelates are known as chelating ligands, and the process is known as chelation.

What is Ligand? 

1. A ligand is a chemical or ionic species that becomes directly linked to the central metal atom or ion during complex formation.
2. Coordinate bonds connect the ligands to the central atom or ion. As a result, ligands are also referred to as the coordinating group, molecule, or ion in a complex ion.
3. The atom in the ligand that can give the electron pair is referred to as the donor atom or the coordinating atom. In ammonia, for example, nitrogen is the donor atom, whereas, in water, oxygen is the donor atom.
4. Electron pairs given by ligands are accommodated in empty orbitals of the central metal atom to form complex ions.

Types of Ligands

One or more donor sites can be detected in a ligand. Ligands can be one of the following categories, depending on the number of donor sites:

1. Monodentate or unidentate ligands
2. Bidentate ligands
3. Polydentate ligands 

A ligand is said to be monodentate if it can only establish one coordinate covalent bond per molecule. If there are two donor sites, the ligand is a ‘bidentate ligand’. The denticity of ligands describes this classification. Because the ligand in a chelate is linked to the central metal atom via two or more donor sites, the ligand is either bidentate or polydentate. The ligand of a chelate is usually cyclic or ring in structure. Chelating agents are another name for these ligands.

Chelating Ligands Meaning

Chelating ligands, also known as ‘multidentate ligands’, are compounds that may make several bonds to a single metal ion. Ethylenediamine and oxalate are two simple (and common) examples.

Chelate

A chelate is a molecule that consists of a central metal atom that is linked to a ligand that has at least two or more donor sites. As a result, the chelate is the entire complex that includes the core metal atom and the ligand. This complex is also known as a coordination compound or coordination complex. A chelate has only one ligand, but certain coordination complexes attach two or more ligands to the central metal atom.

Chelate effect

The metal-ligand relationship is more stable when a ligand forms a ring with a metal ion. In other words, complexes containing chelate rings are more stable than complexes lacking rings, and this is known as the chelate effect.

Ethylenediamine is a well-known chelating ligand (NH₂ CH₂ CH₂ NH₂). Using the two nitrogen atoms present can establish a connection with a metal ion.

Distinction Between a Ligand and a Chelate

The terms ligand and chelate are very closely related. The main difference between ligands and chelates is that ligands are chemical substances that donate or share electrons with a central atom via coordination bonds. In contrast, chelates are compounds with a central atom connected to surrounding ligands.

Conclusion

It is reasonable to conclude that ligands are the fundamental building blocks of coordination molecules. In coordination, a chemical ligand is a molecule or ions that connect with the central metal atom and produce a coordination complex. It functions as an electron-pair donor, whereas the centre atom functions as an electron pair acceptor.

The terms ligand and chelate are often used in coordination chemistry. The main difference between ligands and chelates is that ligands donate or share electrons with a central atom via coordination bonds. In contrast, chelates are compounds with a central atom bonded to surrounding ligands. The creation of a cyclic configuration around the core metal atom is caused by di- and polydentate ligands. Such a cyclic metal complex is known as a chelate, and the ligands that produce chelates are known as chelating ligands, and the process is known as chelation. When a ligand forms a ring with a metal ion, the metal-ligand relationship is shown to be more stable. In other words, complexes containing chelate rings are more stable than complexes lacking rings, and this is known as the chelate effect.