The Metal-rich Phosphide Ce4Ir13.55P9

Needle-shaped crystals of the metal-rich phosphide Ce4Ir13.55P9 were synthesized from the elements in a lead flux (starting composition 1 : 2 : 2 : 60) at 1370 K followed by slow cooling. Ce4Ir13.55P9 crystallizes with a new orthorhombic structure type: Pnma, a = 1269.1(2), b = 399.1(1), c = 3349.9(7) pm, wR2 = 0.0722, 2025 F2 values and 139 variables. Two of the 14 crystallographic iridium sites show small defects. All phosphorus atoms have slightly distorted tricapped trigonal prismatic metal coordination by cerium and iridium. The iridium and phosphorus atoms build up a threedimensional [Ir13.55P9]δ− polyanion in which the cerium atoms fill distorted hexagonal cavities. Within the polyanion the phosphide anions are isolated, and one additionally observes a broad range of Ir–Ir bonding (Ir–Ir distances 278 – 298 pm). From a geometrical point of view the Ce4Ir13.55P9 structure can be considered as an intergrowth structure of distorted ThCr2Si2and SrPtSb-related slabs.