Coordination compounds: ligands, coordination numbers, isomerism, etc.

Coordination Compounds: Ligands, Coordination Numbers, Isomerism, etc.

Introduction
Coordination compounds are an important part of modern chemistry. The study of coordination compounds involves the understanding of the bonding between metals and ligands. Ligands are atoms or molecules that can bond to a metal ion to form a coordination compound. The coordination number refers to the number of ligands that are attached to the central metal ion. Isomerism is a phenomenon where compounds have the same molecular formula but different structures.

Key Concepts

1. Ligands

   • A ligand is an atom, ion or molecule that can bond to a metal ion to form a complex ion.
   • Ligands have a lone pair of electrons that they can share with a metal ion.
   • Common ligands include water, ammonia, chloride ions, and ethene.

2. Coordination Numbers

   • Coordination number is the number of ligands that are attached to the central metal ion.
   • Coordination numbers can range from 2 to 12.
   • The coordination number is determined by the size of the central metal ion and the size of the ligands.

3. Isomerism

   • Isomers are molecules with the same molecular formula but different structures.
   • Isomerism in coordination compounds can be of two types: geometric and optical.
   • Geometric isomers have different spatial arrangements of ligands around the central metal ion.
   • Optical isomers have a non-superimposable mirror image.

Equations and Formulas

1. Coordination Complex

   • A coordination complex is a compound in which a central metal ion is bonded to one or more ligands.
   • [M(Ligand)]n+ is a notation used to denote coordination compounds. M represents the metal ion, Ligand represents the ligands, and n+ represents the charge on the complex.

2. Naming Coordination Compounds

   • The names of coordination compounds follow a certain pattern.
   • The name of the ligand is written first and is followed by the name of the metal ion.
   • The coordination number is denoted by a prefix.
   • For example, [Co(NH3)6]Cl3 is named hexaamminecobalt(III) chloride.

Examples

1. Tetraamminecopper(II) sulfate

   • The formula of tetraamminecopper(II) sulfate is [Cu(NH3)4]SO4.
   • The coordination number of Cu is 4.
   • The ligand is ammonia.
   • The compound is a salt and is blue in color.

2. Dichlorobis(ethylenediamine)cobalt(III) chloride

   • The formula of dichlorobis(ethylenediamine)cobalt(III) chloride is [Co(en)2Cl2]Cl.
   • The coordination number of Co is 6.
   • The ligands are ethylenediamine and chloride ions.
   • The compound is purple in color.

References for Further Learning

1. Cotton, F. A., & Wilkinson, G. (1988). Advanced inorganic chemistry (5th ed.). Wiley.

2. Huheey, J. E., Keiter, E. A., & Keiter, R. L. (1993). Inorganic chemistry: principles of structure and reactivity (4th ed.). HarperCollins.