Coordination Compounds Overview

Coordination Compounds: Overview

• Coordination compounds are compounds containing a central metal ion bonded to one or more ligands.
• Ligands are molecules or ions that coordinate with the metal ion.
• The coordination number of a metal ion is the number of bonds formed between the metal and surrounding ligands.
• The coordination sphere encompasses the central metal ion and its ligands.

Types of Ligands

• Monodentate ligands: These ligands bind to the metal ion through a single donor atom. Examples include chloride ions (Cl-), ammonia (NH₃), and water (H₂O).
• Bidentate ligands: These ligands bind to the metal ion through two donor atoms. Examples include ethylenediamine (en) and oxalate ion (C₂O₄^2-).
• Polydentate ligands: These ligands bind to the metal ion through multiple donor atoms. Examples include EDTA (ethylenediaminetetraacetate), which is a hexadentate ligand.

Naming Coordination Compounds

• The ligands are named alphabetically before the metal.
• Anionic ligands end in -o (e.g., chloro, cyano).
• Neutral ligands retain their names (e.g., ammonia, water).
• Oxidation state of the central metal is indicated in Roman numerals in parentheses.
• The name of the complex is preceded by the prefixes mono-, di-, tri-, tetra-, penta-, and hexa- to indicate the number of ligands.
• The prefixes bis-, tris-, tetrakis-, pentakis-, and hexakis- are used for bidentate and polydentate ligands to show the number of ligands.

Isomerism in Coordination Compounds

• Structural isomers: These isomers differ in the arrangement of ligands around the metal ion.
• Linkage isomers: These isomers differ in the atom of the ligand that bonds to the metal.
• Geometrical isomers: These isomers differ in the spatial arrangement of ligands around the metal ion. Examples include cis and trans isomers.
• Optical isomers: These isomers are non-superimposable mirror images of each other.

Applications of Coordination Compounds

• Catalysis: Coordination compounds are used as catalysts in various reactions.
• Medicinal chemistry: Coordination compounds have several applications in medicine, such as chemotherapy drugs, and as diagnostic tools.
• Industrial processes: Coordination compounds are used in industrial processes such as water treatment and purification.
• Analytical chemistry: Coordination compounds are used in various analytical techniques.

Bonding in Coordination Compounds

• Valence bond theory (VBT): This theory explains the formation of coordination compounds on the basis of hybridization of the central metal ion's orbitals.
• Crystal field theory (CFT): This theory describes the bonding in coordination compounds by considering the interaction between the ligands and the d-orbitals of the metal ion.
• Ligand field theory (LFT): This is an extension of CFT that includes the effect of the bonding on the energies of the metal d-orbitals.

Factors affecting the stability of coordination compounds

• The nature of the metal ion: The size and charge of the metal ion affect the stability of the coordination compound.
• The nature of the ligands: The strength of the ligands affects the stability. Stronger ligands form more stable complexes.
• The pH of the solution: The pH value affects the stability of the compound by influencing the charges of the ions or ligands involved.
• The medium: The nature of the solvent in which the solution is present can affect the stability and reactivity.

IUPAC Nomenclature

• Specific rules are followed to name coordination compounds.
• Ligands are listed alphabetically and their prefixes indicate their number.
• Oxidation state of the metal is represented in parentheses in Roman numerals.
• Anionic ligands end in "-o" and neutral ligands keep their original names.

Structural features of coordination compounds

• Coordination number: The number of ligands attached to the central metal ion.
• Oxidation state: The charge on the central metal ion after considering the charge contributions of the ligands.
• Coordination sphere: The central metal ion and its directly attached ligands.
• Geometries: Linear, square planar, tetrahedral, octahedral are common structures exhibited.