In crystallography, an anti-structure is obtained from a salt structure by exchanging anion and cation positions.  
For instance, calcium fluoride, CaF, crystallizes in a cubic motif called the fluorite structure. The same crystal structure is found in numerous ionic compounds with formula AB, such as ceria (CeO), zirconia (cubic ZrO), uranium dioxide (UO). In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as beryllium carbide (BeC) or lithium oxide (LiO), potassium sulfate (KSO).
Other anti-structures include:
* anti-SnO: TiN
* anti-PbCl: CoP
* anti-CdCl: CoN
* anti-CdI: CsO
* anti-NbS: HfS
* anti-ReO: CuN
* anti-LaF: CuP, CuAs