Anti-structure

 ( Crystallography ) 

[[File:Xtals combined 2 300ppi.png|thumb|right|upright=2|Unit cell of CaF₂, known as fluorite structure, from two equivalent perspectives. 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, CaF₂, crystallizes in a cubic motif called the fluorite structure. The same crystal structure is found in numerous ionic compounds with formula AB₂, such as ceria (CeO₂), Cubic zirconia (cubic ZrO₂), uranium dioxide (UO₂). In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as beryllium carbide (Be₂C) or lithium oxide (Li₂O), potassium sulfate (K₂SO₄).

Other anti-structures include:Peter Paetzold: Chemie. Eine Einführung. de Gruyter, Berlin 2009

• anti-SnO₂: Ti₂N
• anti-PbCl₂: Co₂P
• anti-Cadmium chloride: Co₂N
• anti-Cadmium iodide: Caesium oxide
• anti-NbS₂: Hf₂S
• anti-Rhenium trioxide: Cu₃N
• anti-LaF₃: Cu₃P, Cu₃As

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