PREPARATION AND CRYSTAL-STRUCTURES OF TH5FE19P12 AND THFE4P2

The new compounds Th5Fe19P12 and ThFe4P2 were prepared by reaction of the elemental components in a tin flux and their crystal structures were determined from single-crystal X-ray data. Th5Fe19P12 crystallizes with a new monoclinic structure type: C2/m, a = 2920.3(3), b = 379.18(3), c = 931.48(8) pm, beta = 103.36(1)-degrees, 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 compounds belong to the large family of structures with a metal: nonmetal ratio of exactly or nearly 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 of the prism. In both structures the thorium atoms have trigonal prismatic or octahedral phosphorus coordination. Most iron atoms have the usual tetrahedral phosphorus environment. In addition, the structure of Th5Fe19P12 has iron atoms in rectangular and distorted square pyramidal phosphorus coordination, while the structure of ThFe4P2 contains iron atoms with only two or three phosphorus neighbors.