thumb|right|upright=2|Unit cell of CaF<sub>2</sub>, known as ''fluorite structure'', from two equivalent perspectives.<ref>{{Cite journal|last1=Burr|first1=P. A.|last2=Cooper|first2=M. W. D.|date=2017-09-15|title=Importance of elastic finite-size effects: Neutral defects in ionic compounds|url=https://link.aps.org/doi/10.1103/PhysRevB.96.094107|journal=Physical Review B|volume=96|issue=9|article-number=094107|doi=10.1103/PhysRevB.96.094107|arxiv=1709.02037|bibcode=2017PhRvB..96i4107B }}</ref> In the ''antifluorite structure'' (not shown in picture), the blue positions are taken by the anion, the red positions by the cation.

In crystallography, an '''anti-structure''' is obtained from a salt structure by exchanging anion and cation positions.

For instance, calcium fluoride, CaF<sub>2</sub>, crystallizes in a cubic motif called the fluorite structure. The same crystal structure is found in numerous ionic compounds with formula AB<sub>2</sub>, such as ceria (CeO<sub>2</sub>), zirconia (cubic ZrO<sub>2</sub>), uranium dioxide (UO<sub>2</sub>). In the corresponding ''anti-structure'', called the antifluorite structure, anions and cations are swapped, such as beryllium carbide (Be<sub>2</sub>C) or lithium oxide (Li<sub>2</sub>O), potassium sulfate (K<sub>2</sub>SO<sub>4</sub>).

Other anti-structures include:<ref>Peter Paetzold: Chemie. Eine Einführung. de Gruyter, Berlin 2009</ref> * anti-SnO<sub>2</sub>: Ti<sub>2</sub>N * anti-PbCl<sub>2</sub>: Co<sub>2</sub>P * anti-CdCl<sub>2</sub>: Co<sub>2</sub>N * anti-CdI<sub>2</sub>: Cs<sub>2</sub>O * anti-NbS<sub>2</sub>: Hf<sub>2</sub>S * anti-ReO<sub>3</sub>: Cu<sub>3</sub>N * anti-LaF<sub>3</sub>:<ref>{{Cite journal|last=Mansmann|first=M.|date=1965|title=Über Verbindungen vom Anti-LaF<sub>3</sub>-Strukturtyp|url=https://www.degruyter.com/view/journals/zkri/122/1-6/article-p399.xml|journal=Zeitschrift für Kristallographie - Crystalline Materials|language=en|volume=122|issue=1–6|pages=399–406|doi=10.1524/zkri.1965.122.5-6.399 |bibcode=1965ZK....122..399M |issn=2194-4946|url-access=subscription}}<!--doi is broken 10.1515/zkri-1965-1-639--></ref> Cu<sub>3</sub>P, Cu<sub>3</sub>As

==References== {{Reflist}}

Category:Crystallography