Antifluorite Unit Cell

Study the antifluorite unit cell with the Indigo® 68772W molecular model kit which demonstrates O_h point group symmetry, inverse fluorite crystal structure and tetrahedral coordination of cations by anions. Ideal for solid state chemistry, crystallography, materials science, and electrochemistry (battery cell) courses.

The Indigo® 68772W model kit can build an antifluorite unit cell, the structural inverse of fluorite (CaF₂). Like fluorite, the antifluorite structure belongs to the O_h point group and crystallographic space group Fm3?m, but with the positions of cations and anions reversed. The anions (X^-) form the face-centered cubic sublattice while the cations (A⁺) occupy all eight tetrahedral interstitial sites within the unit cell. Each anion is coordinated to eight cations in a cubic arrangement, while each cation is tetrahedrally surrounded by four anions, giving an 4:8 coordination geometry that directly reflects the 2:1 stoichiometry of A₂X compounds. Classic antifluorite compounds include lithium oxide (Li₂O), sodium oxide (Na₂O), and potassium oxide (K₂O). All are alkali metal oxides whose ionic radii ratios favor the tetrahedral coordination of the smaller cation within the larger anion FCC sublattice.