What is the Difference Between Isostructural and Isomorphous

The key difference between isostructural and isomorphous is that isostructural refers to having a similar crystal structure in which the atoms correspond in position and function, whereas isomorphous refers to being able to crystallize in a form similar to that of another compound or mineral.

Although the terms isostructural and isomorphous sound similar, they are two different chemical terms, describing two different structures in chemistry. We can say that two crystals are isostructural if they have the same structure with or without the same cell dimensions or chemical composition. Methane and ammonium ion are isostructural with each other. Isomorphous materials have the ability to crystallize in a similar way. A good example is the sodium nitrate and calcium sulfate pair.

1. Overview and Key Difference
2. What is Isostructural
3. What is Isomorphous
4. Isostructural vs Isomorphous in Tabular Form
5. Summary – Isostructural vs Isomorphous

What is Isostructural?

Isostructural refers to the property of having similar chemical structures. It is not synonymous with the term isomorphous. We can say that two crystals are isostructural if the two crystals have the same structure but with the same or different cell dimensions and not necessarily the same chemical composition. One can also note comparable variability in the atomic coordinates compared to the cell dimensions and chemical composition. The term isotypic is synonymous with this term.

Some common examples for pairs of isostructural compounds include I-Gold(I) bromide and gold(I) chloride, borazine and benzene, indium(I) bromide and beta-thallium(I) iodide, etc. Moreover, most minerals can be described as isostructural, but they differ in the nature of the cation.

Another similar term to isostructural is isoelectronic. Isoelectronic structures have the same chemical structures. For e.g. methane and ammonium ion are isoelectronic compounds. They are also isostructural because of the tetrahedral structure.

What is Isomorphous?

The term isomorphous refers to the capability to crystallize in a form similar to another compound or mineral. This term is used specifically for substances that are closely related to each other and are able to form end members of a series of solid solutions.

A good example of isomorphous is sodium nitrate and calcium sulfate. This is because both these chemical compounds have similar structures and shapes. We can call some isomorphous substances double salts. However, all these double salts are not isomorphous molecules. Typically, the term isomorphous is used for metals that are completely miscible in each other in their liquid and solid states.

For the identification, two crystals are isomorphous if these compounds have the same space group and unit cell dimensions. In addition, the types and the positions of atoms in both compounds are the same except for the replacement of one or more atoms in a structure with different atomic types in the other compound.

What is the Difference Between Isostructural and Isomorphous?

The key difference between isostructural and isomorphous is that isostructural means having a similar crystal structure in which the atoms correspond in position and function, whereas isomorphous means capable of crystallizing in a form similar to that of another compound or mineral.

The below infographic presents the differences between isostructural and isomorphous in tabular form for side-by-side comparison.

Summary – Isostructural vs Isomorphous

The terms isostructural and isomorphous refer to different structures of minerals in nature. The key difference between isostructural and isomorphous is that isostructural refers to having a similar crystal structure in which the atoms correspond in position and function, whereas isomorphous refers to being able to crystallize in a form similar to that of another compound or mineral.