Preparation and Crystal Structures of Th5Fe19P 12 and ThFe4P2

The new compounds Th5F e19P 12 and ThFe4P2 were prepared by reaction o f the elemental components in a tin flux and their crystal structures were determined from single-crystal X-ray data. Th5F e19P12 crystallizes with a new monoclinic structure type: C2/m, a = 2920.3(3), b = 379.18(3), c = 931.48(8) pm, ß = 103.36(1)°, Z = 2, R = 0.031. ThFe4P2 is isotypic with SmNi4P2: Pnnm, a = 1448.9(2), b = 1074.7(2), c = 376.98(4) pm, Z = 6, R = 0.030. Both com­ pounds belong to the large family o f structures with a m etal: nonmetal ratio o f exactly or near­ ly 2:1. In these phosphides all phosphorus atoms have nine metal neighbors: six are forming a trigonal prism with three additional neighbors capping the rectangular faces o f the prism. In both structures the thorium atoms have trigonal prismatic or octahedral phosphorus coordi­ nation. M ost iron atoms have the usual tetrahedral phosphorus environment. In addition, the structure o f Th5F e19P l2 has iron atoms in rectangular and distorted square pyramidal phos­ phorus coordination, while the structure o f ThFe4P2 contains iron atoms with only two or three phosphorus neighbors.