Synthesis and Structure of the Zintl-Phase K₄Pb₉ Containing Isolated Pb₉^4- Clusters of Two Different Geometries

The first nine-atom deltahedral clusters of lead in the solid state are found in the Zintl-phase K₄Pb₉. The compound crystallizes in the monoclinic space group P2₁/m, Z = 4, with a = 9.648(3) Å, b = 13.243(5) Å, c = 15.909(8) Å, and β = 103.24(4)°. The isolated Pb₉^4- clusters are of two different geometries, a monocapped square antiprism and an elongated tricapped trigonal prism.