The electron-precise Zintl compound RbSb 2 , which was known to melt incongruently at 418°C, has been prepared in pure phase from elemental rubidium and antimony in sealed tantalum crucibles. In accordance with the ribbon-shaped antimonide anions, the compound crystallizes with extremely thin intergrown, mechanically and chemically very sensitive needles of dark-metallic lustre. The crystal structure could be determined and refined using single crystal x-ray data (monoclinic, space group C2/m, a ϭ 1403(2), b ϭ 414.0(4), c ϭ 855.7(14) pm, β ϭ 104.45(12)°, Z ϭ 4, R1 ϭ 0.0901) despite the poor quality of the crystals. It shows fused six-membered rings of two-and three-bonded Sb atoms forming ribbons running along the monoclinic b axis, which can be interpreted as Einleitung