THE ACTINOID NICKEL PHOSPHIDES TH11NI25P20 AND U11NI25P20

The new compounds Th11Ni25P20 and U11Ni25P20 were prepared in a tin fl ux. The crystal structure of Th11Ni25P20 was determined from single-cr ystal X-ray data: Pmmn, a = 392.57(2) pm, b = 3508.7(2) pm, c = 1247.9 (2) pm. Z = 2, R = 0.037 for 883 structure factors and 108 variable pa rameters. The thorium atoms occupy six crystallographic sites with bet ween six and eight phosphorus and nine or ten nickel neighbours. Most nickel atoms have tetrahedral phosphorus environments. The other nicke l atoms have three or five phosphorus neighbours in trigonal planar or square pyramidal arrangement. Most of the phosphorus atoms have trigo nal prismatic metal coordination, which is augmented by two or three m etal atoms outside the rectangular faces of the prisms. Th11Ni25P20 be longs to a large family of structures with a metal:non-metal ratio of about 2:1. The structure contains building elements, which also occur in alpha-ThNi2P2 and UNi3P2. The nickel-nickel bonding is compared wit h that of other ternary nickel phosphides with high nickel content. Th e lattice constants for the isotypic compound U11Ni25P20 are: a = 380. 38(3) pm, b = 3480.4(3) pm, c = 1226.4(1) pm.