Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Inorganic chemistry → Coordination chemistry ↓


Chelation and stability


Chelation and stability are important concepts in the field of coordination chemistry, a branch of inorganic chemistry that deals with the study of complex compounds. These compounds contain a central metal atom or ion bound to a group of surrounding molecules or ions called ligands. Understanding chelation and the associated stability of these complexes involves looking at the nature of the interactions between metal ions and ligands, how these complexes are formed, and why they exhibit certain properties that make them important in many chemical processes.

What is chelation?

Chelation is the process by which a metal ion forms a bond with a molecule having two or more sites that can donate electrons, resulting in a stable ring-like structure known as a chelate ring. The ligands that participate in chelation are called chelating agents. This process can substantially increase the stability of the metal-ligand complex.

A typical chelating agent contains multiple atoms with lone pairs of electrons that can coordinate with the central metal ion. When these atoms form a stable complex with the metal ion, the resulting compound is a chelate. Chelates are unique in their ability to provide increased stability due to the multiple bonds they form with the central metal ion.

Examples of chelating agents

Some common chelating agents include:

  • Ethylenediaminetetraacetic acid (EDTA): EDTA is a well-known chelating agent that can form strong complexes with most metal ions by donating electrons from its four carboxyl and two amine groups.
    • H₂N-CH₂-CH₂-NH-CH₂COOH-CH₂COOH-CH₂COOH-CH₂COOH
  • Citric acid: This tricarboxylic acid forms complexes with metal ions using its three carboxylate groups.
    • C₆H₈O₇
  • Oxalate ion: Known to coordinate with transition metals through its two negatively charged oxygen atoms.
    • C₂O₄²⁻
  • 1,10-Phenanthroline: A bidentate ligand that coordinates using its nitrogen atoms.
    • C₁₂H₈N₂

Stability of chelated complexes

The stability of a chelated complex is often better than that of a non-chelated complex involving the same metal ion. There are several reasons for this increased stability:

  • Entropy and the chelate effect: The formation of a chelate often results in a positive entropy change, which promotes complex formation. The chelate effect is the observation that chelating ligands form more stable complexes than complexes formed by equivalent monodentate ligands.
  • Multiple bonding: Chelating ligands form multiple bonds with the metal ion, leading to increased stability due to the formation of a stable ring system.
  • Ring size and distortion: Five-membered and six-membered rings generally form more stable complexes due to optimal bond angles that minimize distortion.

Factors affecting the stability of the complexes

Several parameters play an important role in determining the stability of metal-ligand complexes:

  • Nature of the metal ion: The charge, size, and electronic configuration of the metal ion can affect complex stability. Complexes involving transition metals are often more stable due to the availability of d-orbitals for bonding.
  • Nature of the ligand: Ligands differ in their ability to donate electrons. Strong field ligands, such as cyanide or carbon monoxide, form more stable complexes than weak field ligands, such as water or ammonia.

Applications of chelation

Chelation and chelated compounds have various applications in different industries, including:

  • Medicine: EDTA is used in chelation therapy to treat heavy metal poisoning, forming stable, non-toxic complexes that are excreted from the body.
  • Agriculture: Chelates are used to provide micronutrients to plants in forms that are easily absorbed.
  • Water treatment: Chelating agents help remove metal ions from water, preventing problems such as scale build-up in boilers.

Conclusion

The stability of chelation and coordination compounds is indispensable for understanding the complex behavior of metal ions and their ligands. The unique properties of chelated complexes arise from several factors, including the chelate effect, ligand nature, and metal ion properties. These complexes have important applications in various fields, contributing to progress in science and industry.


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Chelation and stability

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