Ionization Isomerism

The compounds with the same molecular formula but the different structural arrangement of ligands around the central metal atom are known as isomers and the phenomenon is known as isomerism.

They can be two or more and have similar or different physical and chemical properties. 

The roots of the word isomer are Greek—isos plus meros, or “equal parts.” Isomerism term is related to the compounds which can exist in two or more forms differing in their chemical structure. The term isomerism was given by Swedish chemist Jacob Berzelius in the year 1830.

Isomerism in coordination compounds is mainly divided into two types.

1. Structural isomerism 

2. Stereoisomerism

There are also two general types of isomers

1. Constitutional isomers 

2. Stereoisomers

Ionization isomerism is part of structural isomerism and we are going to study ionization isomerism briefly in this article.

Structural isomerism and its type 

Structural isomerism is a type of isomerism in which the atoms present in compounds are completely arranged in a different order with the same molecular formula.

In structural isomerism the molecules which have the same kind of molecular formula with different connectivities depending upon the order they are put together are present. Structural isomerism is known as the most radical type of isomerism.

Example of structural isomerism 

Butanol H3C-(CH2)3–OH, methyl propyl ether H3C–(CH2)2–O–CH3  , and Diethyl ether (H3C–CH2–)2O have the same molecular formula C4H10O but all three are different structural isomers. 

Ligands are similar in isomers, but they are differently bonded to the central metal atom.

Structural isomerism is divided into 4 types.

Ionization isomerism 

In this type of isomerism, interchange of ligands takes place between coordination and the ionization sphere. They have the same molecular formula but give different ions in solution. 

Linkage Isomerism

Linkage isomerism is shown by coordination compounds that have ambidentate ligands; this type of isomerism occurs due to a change of Donor atom due to ambidentate ligands.

Coordination Isomerism

Coordination isomerism occurs in those coordination compounds in which cation and anion both present as a complex. It takes place due to the interchange of ligands between two complexes.

Hydration or Solvate Isomerism

Hydration isomerism is present in those coordination complexes in which the number of water molecules is different; water molecules are present in coordination and the ionization sphere. This type of isomerism is known as solvent isomerism.

Ionization isomerism 

The complex compounds which have the same composition but from different ions in an aqueous solution are known as ionization isomers and this phenomenon is known as ionization isomerism.

Ionization isomerism can apply to metal complexes, ionisation isomerism relates to the way in which ligands get attached to the metal ion of these complexes.

The importance of ionization isomerism is that it involves an exchange of ions inside and outside the coordination sphere.

In ionization isomerism compounds give different ions in solution to the exchange of ions in the coordination sphere and the counter ion present in the complex.

Hydration or Solvate Isomerism is a special type of ionization isomerism.

 The best example of this occurs for chromium chloride “CrCl3.6H2O” which may contain 4, 5, or 6 coordinated water molecules.

[CrCl2(H2O)4]Cl.2H2O is bright green in colour.

[CrCl(H2O)5]Cl2.H2O is grey in colour.

[Cr(H2O)6]Cl3 violet in colour.

Ionization isomers are known as complex salts which have the same chemical formula but give different ions when the complex is electrolyzed.

Examples of ionization Isomerism 

1.[Co(NH3)5Br]SO4 and [Co(NH3)5 SO4]Br

     Violet.                        Red

They give SO42- and Br- respectively in the aqueous solution. Violet coloured complex gives a white precipitate with BaCl2    solution whereas red coloured complex gives a yellow precipitate with AgNO3.

2. Another example is, [Pt(NH3)4(OH)2]SO4 and [Pt(NH3)4SO4](OH)2.

This happens because the arrangement of ions is dissimilar in a solution. 

For example,

[PtBr(NH3)3]O2NO2 (anion in solution)

[Pt(NO2)(NH3)]Br (anion in solution)

3.[CoBr(H2O)]Cl and [CoCl(H2O)]Br

They both give different types of ions we dissolved into an aqueous solution.

4.[Cr(NH3)5(OSO3)]Br and [Cr(NH3)5Br]SO4

In this Br– and SO4 can exchange their positions between coordinate sphere and also from ionization sphere, hence it shows ionization isomerism.

Conclusion 

The study of isomerism plays an important role in the analysis of similar complexes which have different properties. Cisplatin has a therapeutic role in cancer while transplatin is toxic. Although they both have the same molecular and structural formula, the only difference is the arrangements of ligands. 

Isomers differ in the structural arrangement of atoms in space. In the chemistry of air pollution, isomers are very significant because of their drastic variation in chemical and physical properties. Isomers are very useful in the field of medicine and nutrition because they start to work on isomers over another, so its state that isomers are very important for the development of pharmaceutical industries.