Coordination Compounds – JEE Mains Chemistry
1. Introduction to Coordination Compounds
Coordination compounds are compounds in which a central metal atom or ion is bonded to surrounding ligands (ions or molecules) via coordinate covalent bonds. These compounds play an important role in various chemical processes and have applications in different fields, such as biology and metallurgy.
2. Werner’s Theory
Werner’s theory explains the formation of coordination compounds. It states that a central metal atom can form bonds with ligands in two types of coordination: primary and secondary. The primary valency refers to the number of bonds formed by the metal ion with the ligands, while the secondary valency refers to the spatial arrangement of the ligands around the metal ion.
3. Ligands
Ligands are ions or molecules that donate a pair of electrons to the central metal atom or ion to form coordinate bonds. Ligands can be classified as:
- Monodentate: Ligands that form one bond with the metal (e.g., H₂O, NH₃).
- Bidentate: Ligands that form two bonds with the metal (e.g., ethylenediamine, en).
- Polydentate: Ligands that form more than two bonds with the metal (e.g., EDTA).
4. Coordination Number
The coordination number of a metal ion in a coordination compound is the number of coordinate bonds formed between the central metal atom and the surrounding ligands. This number depends on the size, charge, and electronic configuration of the metal ion and the nature of the ligands.
5. Denticity and Chelation
Denticity refers to the number of bonds a ligand can form with the metal center. Chelation occurs when a polydentate ligand forms multiple bonds with a metal, creating a stable ring-like structure around the metal. Chelating agents, like EDTA, are widely used in coordination chemistry due to their ability to form stable complexes.
6. IUPAC Nomenclature of Mononuclear Coordination Compounds
The IUPAC nomenclature of coordination compounds involves naming the ligands first (prefixes indicating the number of each ligand) followed by the name of the central metal ion with its oxidation state in parentheses. For example, in [Cu(NH₃)₄]SO₄, the name is tetraammine copper(II) sulfate.
7. Isomerism in Coordination Compounds
Coordination compounds exhibit different types of isomerism, including:
- Structural Isomerism: Isomers differ in the arrangement of ligands around the metal center (e.g., linkage isomerism, ionization isomerism).
- Stereoisomerism: Isomers differ in the spatial arrangement of ligands (e.g., geometric and optical isomerism).
8. Bonding: Valence Bond Approach
The Valence Bond Theory explains the bonding in coordination compounds by considering the overlap of orbitals from the metal ion and the ligands. The metal ion uses its hybrid orbitals to bond with the ligands. This approach helps in understanding the geometry and bonding in complex molecules.
9. Crystal Field Theory
Crystal Field Theory (CFT) explains the splitting of d-orbitals in a metal ion in the presence of ligands. The theory suggests that ligands cause a distortion in the degenerate d-orbitals of the metal, resulting in energy splitting. This theory helps explain the magnetic properties and color of coordination compounds.
10. Colour and Magnetic Properties
The color of coordination compounds arises from the d-d transitions in metal ions when they absorb light. The magnetic properties are related to the number of unpaired electrons in the metal ion's d-orbitals. For example, a compound with unpaired electrons exhibits paramagnetism, while one with paired electrons is diamagnetic.
11. Importance of Coordination Compounds
Coordination compounds have wide-ranging applications:
- Qualitative Analysis: Coordination compounds are used to identify metal ions in analytical chemistry.
- Extraction of Metals: Complex formation plays a role in the extraction of metals like gold, silver, and copper.
- Biological Systems: Coordination compounds are essential in biological systems, for example, the role of hemoglobin in transporting oxygen in blood.