The Metal-rich phosphide C_e4Ir_(13.55)P_9

摘要

Needle-shaped crystals of the metal-rich phosphide Ce_4Ir 1_(3.55)P_9 were synthesized from the elements in a lead flux (starting composition 1 : 2 : 2 : 60) at 1370 K followed by slow cooling. Ce_4Ir_(13.55)P_9 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 F~2 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 [Ir (13.55)P_9]~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 Ce_4Ir_(13.55)P_9 structure can be considered as an intergrowth structure of distorted ThCr2Si2- and SrPtSb-related slabs.