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Understanding Coordination Complex Isomerism: Types and Examples

Coordination Complex Isomerism: Understanding the Different Types

In chemistry, isomerism is the existence of two or more chemical compounds with the same chemical formula but different structures or configurations. Coordination complex isomerism, also known as stereo isomerism, is a type of isomerism that occurs in coordination complexes.

Coordination complexes are molecules that are made up of a central metal ion and a surrounding array of ligands. In this article, we will delve into the different types of coordination complex isomerism and provide examples to help you understand them.

Types of Isomerism

There are two types of isomerism in coordination complexes; structural isomerism and stereo isomerism. Structural isomerism occurs when there are different ways to arrange the atoms within the molecule.

Stereo isomerism occurs when the atoms are arranged in the same order, but their three-dimensional (3D) orientation in space is different. There are two types of stereo isomerism: geometrical isomerism and optical isomerism.

Geometrical isomerism occurs in coordination complexes when the ligands attached to the central metal ion cannot rotate around the metal-ligand axis. For example, cisplatin and transplatin are two geometrical isomers of platinum (II) diammine dichloride.

In cisplatin, the two chloride ligands are adjacent to each other, while in transplatin, the two chloride ligands are on opposite sides of each other. Optical isomerism, also called enantiomerism, occurs when the ligands attached to the central metal ion form a chiral arrangement.

Chiral molecules are mirror images of each other that cannot be superimposed on each other. For instance, [Co(NH3)5Cl]2+ and [Co(NH3)5Br]2+ are optical isomers since they have a chiral arrangement of five ammonia molecules and one halide ligand surrounding a cobalt ion.

Ionisation Isomerism Examples

Ionisation isomerism is a type of structural isomerism that occurs in coordination complexes where the ligand and counter ion can exchange positions in an equatorial plane. This occurs when the counterion usually forms a weak bond with the central metal ion, allowing it to easily dissociate from the coordination sphere.

This type of isomerism does not require any change in the coordination number of the central metal atom and is generally distinguished by the physical properties of the isomers. Lets take a look at some examples.

Example 1: [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br

These isomers have the same chemical formula, [Co(NH3)5Br]SO4, but a different arrangement of ligands. The sulphate ion and the bromide ion have exchanged their positions in the coordination sphere.

[Co(NH3)5Br]SO4 is yellow in color and on reaction with silver nitrate and barium chloride form white precipitates of AgBr and BaSO4, respectively. [Co(NH3)5SO4]Br has the opposite color, purple, and on reaction with silver nitrate and barium chloride, form white precipitates of Ag2SO4 and BaBr2.

The color difference is due to the presence of different counter ions in the complex. Example 2: [Cr(NH3)5Br]Cl and [Cr(NH3)5Cl]Br

These isomers have the same chemical formula, [Cr(NH3)5Br]Cl, but with different ligand arrangements.

In [Cr(NH3)5Br]Cl, the bromide ion is in the coordination sphere, while the chloride ion is the counter ion. In [Cr(NH3)5Cl]Br, chloride and bromide ions have swapped their positions.

The two isomers have different colors, [Cr(NH3)5Br]Cl is red and [Cr(NH3)5Cl]Br is violet. Example 3: [Fe(NH3)SO4]CN and [Fe(NH3)CN]SO4

Both isomers have the same chemical formula of [Fe(NH3)SO4]CN but with different arrangements of ligands.

In [Fe(NH3)SO4]CN, the sulphate ion is inside the coordination sphere while in [Fe(NH3)CN]SO4, it is outside the coordination sphere. [Fe(NH3)SO4]CN forms a white precipitate with silver nitrate, while [Fe(NH3)CN]SO4 forms a yellow precipitate with silver nitrate.

Conclusion

In conclusion, isomerism is an essential concept in coordination chemistry. Structural isomerism occurs when two or more chemical compounds have the same chemical formula but different structural arrangements.

Stereo isomerism occurs when the chemical compounds have the same structural arrangement, but their 3D orientation in space is different. Ionisation isomerism is a type of structural isomerism that occurs when the position of the ions interchange, but the arrangement of the ligand around the central metal ion remains the same.

Understanding these concepts will help you appreciate the diversity of coordination complexes and how they interact with other chemical compounds. Coordination complex isomerism is an essential concept in coordination chemistry that occurs when two or more chemical compounds have the same chemical formula but different structural arrangements.

It is divided into two types of isomerism – stereo isomerism and structural isomerism. Stereo isomerism occurs when the atoms are arranged in the same order, but their 3D orientation in space is different.

Structural isomerism occurs when there are different ways to arrange atoms within the molecule. Ionisation isomerism is a type of structural isomerism that is essential to understand in coordination complex isomerism.

FAQs have been included to address common reader queries and help promote understanding of the concept. Coordination complex isomerism provides us with a deeper understanding of the different configurations that coordination complexes can take and their interactions with other chemical compounds.

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