Hello, reders welcome to chemwhite.com today i am going to example about chelate effect and their examples.

What is chelate effect?

Development of stability of an matel when the ligands are attached to the matel. and due to this development of the formation of chelate ring in matel by polydendate ligands in known as chelete effect. this type of formation of chelete ring gives more stability for matel.

Ligands are molecules or ions that can bond to a central metal atom or ion, forming what is known as a coordination complex.

These complexes are vital in many biological and chemical processes.

In the case of the chelate effect, certain ligands exhibit a unique ability to bind to a metal ion at multiple sites simultaneously.

This simultaneous binding creates a more stable and rigid structure compared to simple monodentate ligands, which bond at only one site.

for examples,


[CO (en) 6]3+ – More stability (one or more chelate ring) but

[CO (NH3)6]3+ – less stability (without chelate ring)

So, we can say that, the coordinate compound or complex containing chelete ring is really more stable compair with without chelete ring.

The key to the chelate effect lies in the formation of a cyclic structure, known as a chelate ring or a macrocyclic ring, between the ligand and the metal ion.

This ring formation brings the metal ion into close proximity with the coordinating atoms of the ligand, resulting in a more efficient and stronger bond.

The chelate effect relies on the coordination chemistry principles, including the Lewis acid-base theory, where the metal ion acts as the Lewis acid, accepting electron pairs from the ligand (Lewis base).

Chelation – When Polydentate ligand attached in the central metals atom, making a closed or ring structure. this phenomenon is called chelation.

Condition of chelation – When the complex is formed in a chelation form complex should be have following conditions.

  1. Complex should be at least Polydentate ligand. which make closer or ring type structure around the center metal atoms.
  2. Central metals atoms must required two Or more positive oxidation state.
  3. Chelete ring must be stabilized the complex.

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Chelete ligands

Chelating ligands, often referred to as chelates or chelating agents, are chemical compounds that have the ability to form coordination complexes with metal ions.

When the ligand are attached in the central matel atohis is known as chelete ligands.We can see that central matel atom (Cu)2+ are attached to ligands. and this attachment is known as chelete ligands. and this hole complex is know as chelete.

These ligands possess multiple donor atoms capable of coordinating to the metal center, creating a stable ring-like structure known as a chelate.

Chelating ligands play a significant role in various fields, including chemistry, biochemistry, medicine, and industrial applications.

They are widely used in coordination chemistry to stabilize and control the reactivity of metal ions. Some common examples of chelating ligands include:

  1. Ethylenediaminetetraacetic acid (EDTA): EDTA is a versatile chelating agent with four carboxylic acid groups and two amine groups, capable of binding to metal ions in a hexadentate manner. It forms stable complexes with a wide range of metal ions, including calcium, magnesium, and transition metals.
  2. Nitrilotriacetic acid (NTA): NTA is similar to EDTA and can form stable complexes with metal ions. It is commonly used in metal chelation chromatography and in the removal of heavy metals from industrial waste.
  3. 1,10-Phenanthroline: This aromatic ligand contains two nitrogen atoms capable of binding to metal ions. It forms stable complexes with a variety of transition metal ions and is often used in analytical chemistry and biological research.
  4. Dipyridyl: Dipyridyl is another bidentate ligand with two nitrogen donor atoms. It forms complexes with various metal ions and is frequently employed in coordination chemistry and catalysis.
  5. Dimethylglyoxime (DMG): DMG is a bidentate ligand that forms stable complexes with several transition metals, including nickel. It is widely used in qualitative and quantitative analysis of metal ions.

Chelate ring

When ligands bind to the central metal ion, it forms ring of atoms. or When ligands are attached (bind) to the central metal ions, they form chelete ring of atoms. this chelete ring give more stability. Most of chelete ring contain >4 and <8 atom members.

To determine the number of chelete ring when the ligand bind with the central metal.

A chelate ring, also known as a chelation ring, refers to a cyclic structure formed by the coordination of a central metal ion with two or more donor atoms.

The donor atoms are typically from a ligand or a molecule that can bind to the metal ion through coordinate covalent bonds.

The term “chelate” originates from the Greek word “chele,” which means “claw,” alluding to the grasp-like interaction between the metal ion and the ligand.

In a chelate ring, the ligand forms multiple bonds with the metal ion, usually through two or more electron pairs.

This coordination can involve various types of donor atoms, such as nitrogen, oxygen, sulfur, or phosphorus. Common ligands that form chelate rings include amino acids, porphyrins, and macrocyclic compounds.

The chelate ring formation enhances the stability of the metal-ligand complex compared to a simple monodentate complex where the ligand binds to the metal ion through only one donor atom.

The chelation effect arises from the additional bonds formed between the metal ion and the ligand, which results in a more rigid and stable structure.

This increased stability can have important implications in various fields, including coordination chemistry, bioinorganic chemistry, and medicinal chemistry.

Chelate rings find numerous applications in various areas of science and technology.

For example,

In medicine, chelation therapy utilizes chelating agents that can form stable chelate rings with metal ions to treat heavy metal poisoning. In catalysis, chelate ligands are often used to stabilize metal catalysts and enhance their reactivity and selectivity.

Chelation processes also play a vital role in biological systems, such as metalloproteins and enzymes, where metal ions are coordinated within chelate rings to perform specific functions.

Differance between monodentate ligands and chelating ligands

Monodentate ligands – the best example for monodentate ligads is,

  • Monodentate ligands are molecules or ions that can form a single bond with a metal atom or ion.
  • They have only one atom capable of donating a lone pair of electrons to the metal center.
  • Examples of monodentate ligands include water (H2O), ammonia (NH3), chloride ion (Cl-), and cyanide ion (CN-).
  • Each monodentate ligand forms a single coordinate bond with the metal, meaning it donates only one pair of electrons to the metal center.

Chelating ligands – chelete ligands is like ethylenediamine. In this case it form five or six membered ring. but chelete complex are more stable then the analogous complex with monodentate ligands. there are several key point for cheating ligands, they are,

  • Chelating ligands are molecules or ions that can form multiple bonds with a metal atom or ion.
  • They have multiple atoms capable of donating lone pairs of electrons to the metal center.
  • Chelating ligands typically contain a donor atom capable of forming more than one bond with the metal center, and they often possess a flexible or cyclic structure.
  • The multiple bonds formed by chelating ligands create a ring-like structure known as a chelate.
  • Examples of chelating ligands include ethylenediamine (en), 1,2-diaminocyclohexane (DACH), ethylenediaminetetraacetic acid (EDTA), and oxalate ion (C2O4^2-).
  • Chelating ligands can form stronger and more stable complexes with metal ions due to their ability to provide multiple coordinating atoms, resulting in enhanced stability and specificity.
  • for examples – Ethylenediamine

What are the fector effecting stability of complexes?

  1. Size of ring
  2. Matter chelete showing 5 mamber ring are more stable and chelete having 6 mamber ring are slightly less stable.
  3. 6 mamber chelete having unsaturation are more stable then 5 mamber chelete.
  4. Ring of other sizes grater then 6 are none. but these are unstable and show little chelete effect. reson is bulkiness. It mean it give little chelete.
  5. No of chelete ring – no of chelete ring increase stability of complex increase.

Steric effect

The steric effect is also significant in the stability. If the stability of chelete complex decrease then the steric fector increase.

The steric fector effect of complex depend upon on the bulkyness of ligands.

The complex with 2 methyl B hydroxy quinolene is less stable then B hydroxy quinolene. reson is bulkyness , it persent very near to donor atom.

for examples,

(N) atom

You can see, N atom is very near to donor atom, that is the reson it is bulkyness.

Application of chelete complex in chemistry

  1. It is used nickel DMG formation. it is a chelete complex. this complex give red ppt. it is confirmative test of Ni.
  2. Mg, Al, Zn is the give ppt. with B hydroxy quinolene. this complex appear specific colour.
  3. According to biological Science, – Vitamin B12 is a chelete complex of cobalt. Cytochroms which are electron carrier are iron chelete. Plastocyanin which are also electron carrier.
  4. The chelate effect finds applications in various fields, demonstrating its wide-ranging significance. Here are a few notable examples:
  5. Medicinal Chemistry: Chelation therapy involves the use of chelating agents to remove toxic metals from the body. These agents form stable chelate complexes with metal ions, facilitating their excretion. Chelation therapy is particularly effective in treating heavy metal poisoning and certain medical conditions like Wilson’s disease and thalassemia.
  6. Coordination Chemistry: The chelate effect plays a crucial role in designing and synthesizing coordination complexes for catalysis, molecular recognition, and drug development. Chelating ligands can enhance the stability and reactivity of metal catalysts, improving their efficiency in various chemical reactions.
  7. Environmental Science: Chelating agents are employed in environmental remediation to remove metal contaminants from soil and water.

Factors Influencing the Chelate Effect

Several factors influence the strength and stability of chelate complexes. One crucial factor is the size of the chelate ring.

Generally, larger rings tend to form more stable complexes due to the increased number of coordinating atoms and a greater spatial constraint on the metal ion.

The nature of the coordinating atoms and their ability to donate electron pairs also plays a significant role.

You know, Nitrogen, oxygen, and sulfur atoms are commonly found in chelating ligands due to their high electron-donating capabilities.

Another crucial aspect is the geometry of the chelate complex.

The rigidity of the chelate ring often forces the metal ion into a specific arrangement, influencing the overall shape of the complex.

This geometric constraint can have profound effects on the reactivity, selectivity, and catalytic properties of the chelate complex. Furthermore, the charge and charge distribution within the chelating ligand can significantly affect the binding affinity and stability of the complex.


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