Detailed Notes on Coordinate Compounds for JEE Exam Preparation

1. Double Salts:

• Definition: Double salts are compounds that contain two different cations and two different anions in a single crystal lattice. For example: KAl(SO₄)₂.12H₂O (potassium aluminum sulfate dodecahydrate).

• Formation and stability: Double salts are formed when two different salts can crystallize together without undergoing a chemical reaction. The stability of double salts depends on several factors, including the size and charge of the ions, the lattice energy of the compound, and the solubility of the individual salts.

• Coordination number and geometry: The coordination number of a metal ion in a double salt is determined by the number of ligands coordinated to it. The geometry of the complex depends on the coordination number and the type of ligands.

• Isomorphism and polymorphism: Isomorphism is the phenomenon of two or more compounds having the same crystal structure. Polymorphism is the phenomenon of a compound existing in two or more different crystal structures. Double salts can exhibit isomorphism and polymorphism depending on the conditions under which they are crystallized.

2. Complex Compounds:

• Definition: Complex compounds are compounds that contain a central metal ion coordinated to ligands. Ligands are molecules or ions that donate electrons to the metal ion and form coordinate covalent bonds. For example: [Co(NH₃)₆]Cl₃ (cobalt hexammine chloride).

• Werner’s theory: Werner’s theory proposed that the metal ion in a complex compound is surrounded by a fixed number of ligands, which are arranged in a specific spatial arrangement. This arrangement is known as the coordination sphere.

• Valence bond theory: Valence bond theory explains the bonding in complex compounds by considering the overlap of atomic orbitals of the metal ion and the ligands. This theory provides a qualitative understanding of the bonding and geometry of complex compounds.

• Crystal field theory: Crystal field theory explains the bonding and properties of complex compounds by considering the interactions between the metal ion and the ligands in terms of electrostatic interactions and ligand field effects. This theory provides a more quantitative understanding of the bonding and properties of complex compounds.

• Magnetic properties: The magnetic properties of complex compounds depend on the number of unpaired electrons in the metal ion. Complex compounds with unpaired electrons are paramagnetic, while those with no unpaired electrons are diamagnetic.

• Isomerism: Isomerism is the phenomenon of compounds having the same molecular formula but different structures. Coordination compounds can exhibit various types of isomerism, including structural isomerism, linkage isomerism, and geometrical isomerism.

• Nomenclature: The nomenclature of coordination compounds follows a systematic set of rules, which includes specifying the name of the central metal ion, the ligands, and the oxidation state of the metal ion.

3. Ligands:

• Definition: Ligands are molecules or ions that donate electrons to a metal ion and form coordinate covalent bonds. Ligands can be classified into various types based on their structure and properties.

• Classification based on denticity: Ligands can be classified as monodentate, bidentate, tridentate, etc., based on the number of donor atoms they can use to bind to a metal ion.

• Chelating ligands: Chelating ligands are ligands that can bind to a metal ion through more than one donor atom. Chelating ligands form stable complexes and play an important role in many biological processes.

• Polydentate ligands: Polydentate ligands are ligands that have multiple donor atoms and can bind to more than one metal ion. Polydentate ligands play an important role in the formation of coordination polymers and metal complexes with high stability.

4. Metal-Ligand Bonding:

• Types of metal-ligand bonds: There are various types of metal-ligand bonds, including ionic bonds, covalent bonds, coordinate covalent bonds, and hydrogen bonds. The type of bond that forms depends on the nature of the metal ion and the ligand.

• Factors affecting the strength of metal-ligand bonds: The strength of metal-ligand bonds is influenced by several factors, including the charge and size of the metal ion, the basicity and size of the ligand, and the presence of other ligands in the coordination sphere.

• Stability of coordination compounds: The stability of coordination compounds depends on the strength of the metal-ligand bonds, the number of ligands coordinated to the metal ion, and the overall charge of the complex.

5. Applications of Coordination Compounds:

• Coordination compounds in qualitative and quantitative analysis: Coordination compounds are used as reagents in qualitative and quantitative analysis of various metal ions. For example, EDTA (ethylenediaminetetraacetic acid) is used as a chelating agent to determine the concentration of metal ions in a solution.

• Coordination compounds as catalysts in various industrial processes: Coordination compounds are used as catalysts in various industrial processes, such as the production of polyethylene, polypropylene, and other polymers. They also play an important role in the refining of petroleum and the production of pharmaceuticals.

• Coordination compounds in medicine: Coordination compounds have numerous applications in medicine, including chelation therapy, metal-based drugs, and contrast agents for medical imaging. For example, cisplatin is a coordination complex that is used as an anticancer drug.

• Coordination compounds in photography and imaging techniques: Coordination compounds are used in photography and imaging techniques, such as the development of photographic films and the production of color dyes.

6. Organometallic Compounds:

• Definition: Organometallic compounds are compounds that contain at least one bond between a metal atom and a carbon atom. Organometallic compounds can be classified into various types based on the nature of the metal-carbon bond.

• Bonding in organometallic compounds: The bonding in organometallic compounds can be explained using various theories, including the valence bond theory, the molecular orbital theory, and the Dewar-Chatt-Duncanson model.

• Classification of organometallic compounds: Organometallic compounds can be classified based on the type of metal-carbon bond, such as sigma complexes, pi complexes, and metal carbonyls.

• Applications of organometallic compounds: Organometallic compounds have numerous applications in catalysis, the synthesis of organic compounds, and pharmaceuticals. For example, Ziegler-Natta catalysts are organometallic compounds that are used in the production of polyethylene and polypropylene.

NCERT References:

• NCERT Chemistry Class 11:

• Chapter 10: The s-Block Elements

• Chapter 11: The p-Block Elements

• NCERT Chemistry Class 12:

• Chapter 9: Coordination Compounds

• Chapter 10: Haloalkanes and Haloarenes

• Chapter 12: Aldehydes, Ketones and Carboxylic Acids