Compounds formed from C₆₀ and potassium: K₆C₆₀ and K₃C₆₀

a) Arrangement of C₆₀ molecules in a face-centred cubic lattice.

b) K₆C₆₀, with a body- centred cubic unit cell with C₆₀⁻ molecular ions at the cell corners and body centre, and K⁺ ions occupying half of the sites in the faces of the cell which have approximate tetrahedral coordination to four C₆₀ molecular ions.

c) K₃C₆₀ is obtained by filling all the tetrahedral and all the octahedral holes in the close-packed C₆₀³⁻ lattice with K⁺ ions.

Cesium forms similar  body centred cubic structures.