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Coordination Chemistry: Isomers

A coordination compound or complex ion is a molecule that contains a central metal ion to which are attached one or more ligands. In many complexes there is more than one way in which the ligands may be attached to or arranged around the metal center.

Isomers are compounds that have the same molecular formula but possess different arrangements of atoms. Two isomers are non-superimposable, which means that one cannot mentally have the two compounds occur the same space with each atom in one isomer perfectly coinciding with the same atom in the other isomer.

The scheme and definitions provided below are commonly used to classify coordination chemistry isomers.

Isomerization in Coordination Compounds

Structural Isomers
Coordination Isomers or Ionization Isomers
Linkage Isomers
Diastereomers or Geometric Isomers
Enantiomers or Optical Isomers


The following four pages provide examples of each type of isomerization: coordination, linkage, geometric, and optical.
For each type of isomerization, carefully examine the structures of each pair of molecules and answer the following questions:

  1. What makes the two molecules different?
  2. What is the key concept associated with each type of isomerization?
  3. Formulate a definition for each type of isomerization.

The molecules may be shown in ball-and-stick or space-filling formats. The ball-and-stick format represents each atom with a small ball (an especially small ball is used for hydrogen atoms) and uses a stick to show a chemical bond. The space-filling format represents each atom with a sphere that reflects the atom's van der Waals radius. The sum of the van der Waals radii for two atoms not bonded to each other roughly represents the distance of closest approach for the two atoms. Thus the space-filling model provides an estimate of the size of the molecule and its "surface".

Coordination Isomers
Linkage Isomers
Geometric Isomers
Optical Isomers

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© Copyright 2008 David N. Blauch