The key difference between fluorite and antifluorite structure is that fluorite has a CCP cation array and tetrahedral anions, whereas antifluorite structure has an inverse structure with an anion array and tetrahedral cations.
Fluorite and antifluorite are ionic arrangements of different ionic compounds with similar arrangements and different electron locations. Fluorite structure has an arrangement completely opposite to that of antifluorite structure.
CONTENTS
1. Overview and Key Difference
2. What is a Fluorite Structure
3. What is an Antifluorite Structure
4. Fluorite vs Antifluorite Structure in Tabular Form
5. Summary – Fluorite vs Antifluorite Structure
What is Fluorite Structure?
Fluorite structure is the motif of compounds having the chemical formula MX2. This term is mainly used in solid-state chemistry. The X in this chemical formula gives the eight tetrahedral interstitial sites, and the M is an ion that occupies the regular sites of an FCC (face-centered cubic structure). In other words, the cations in this ionic crystal structure have an expanded face-centered cubic arrangement, and the anions occupy both types of tetrahedral holes. Moreover, the cations have a coordination number of 8, whereas the anions have a coordination number of 4. Common mineral fluorites usually have this structure. CaF2, BaCl2, and PbO2 are a few examples.
Figure 01: Calcium Fluoride Compound Structure with Fluorite Arrangement
We can use crystallography ( a strong and powerful tool in investigating the structure of crystalline materials) to determine this structure, and we can understand the crystal structure of various materials to determine the structure-property relationship, which is helpful in predicting the behavior of crystalline materials. Moreover, we can use these properties to introduce the ability to tune the properties.
A common example of a fluorite structure is calcium fluoride, where we can obtain the crystallographic data using X-ray diffraction to get the locations of electron density of crystal structures. Moreover, there are some modern software applications, including Olex2, we can use to solve the crystal structure of crystallographic output files.
What is Antifluorite Structure?
Antifluorite structure is the motif for compounds having the chemical formula M2X. This type of arrangement has locations of anions and cations, which are reverse compared to fluorite structures. These anions tend to occupy FCC regular sites. The cations tend to occupy tetrahedral interstitial sites.
Figure 02: The Antifluorite Arrangement of Magnesium Silicide
Commonly, this is called the opposite arrangement because it is the opposite of the fluorite structure. Some examples of compounds with an antifluorite structure include K2O, Li2O, Na2O, K2S, and Na2S. In these compounds, the anions and cations are swapped. In other words, the crystal structure in antifluorite compounds is identical to the fluorite arrangement, but the positions of the cations and anions appear to be reversed.
What is the Difference Between Fluorite and Antifluorite Structure?
Fluorite and antifluorite compounds are important arrangements of ions in ionic compounds (cations and anions) according to stability and other factors. The key difference between fluorite and antifluorite structure is that fluorite has a CCP cation array and tetrahedral anions, whereas antifluorite structure has an inverse structure with an anion array and tetrahedral cations. Thus, fluorite structure is the opposite of antifluorite structure. CaF2, BaCl2, and PbO2 are some examples of compounds with a fluorite structure whereas K2O, Li2O, Na2O, K2S, and Na2S are some examples of compounds with an antifluorite structure.
The below infographic presents the differences between fluorite and antifluorite structure in tabular form for side-by-side comparison.
Summary – Fluorite vs Antifluorite Structure
Fluorite structure is the motif of compounds having the chemical formula MX2. Antifluorite structure is the motif for compounds having the chemical formula M2X. The key difference between fluorite and antifluorite structure is that fluorite has a CCP cation array and tetrahedral anions, whereas antifluorite structure has an inverse structure with an anion array and tetrahedral cations.
Reference:
1. “6.11D: Structure – antifluorite.” Chemistry LibreTexts. Retrieved November 27, 2022.
Image Courtesy:
1. “Fluorite Structure” By ShutterWaves – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Antifluorite Structure” By ShutterWaves – Own work (CC BY-SA 4.0) via Commons Wikimedia