Actinoid transition metal phosphides An2T12P7 (An = Th, U; T = Fe, Co, Ni) and arsenides An2T12As7 (An = Th, U; T = Co, Ni) with Zr2Fe12P7 type structure

Abstract

The preparation and the lattice parameters for the ten title compounds with Zr₂Fe₁₂P₇ type structure are reported; six of them for the first time. The crystal structures of the phosphides Th₂Fe₁₂P₇ (a = 917.3(1) pm, c = 372.2(1) pm), U₂Fe₁₂P₇ (a = 908.7(2) pm, c = 364.1(1) pm) and U₂Ni₁₂As₇ (a = 935.9(1) pm, c = 383.5(1) pm) were refined in the space group P (Nr. 174), where all atomic positions are fully occupied. In contrast, the structure refinements of the phosphides Th₂Co₁₂P₇ (a = 912.8(1) pm, c = 370.5(2) pm) and U₂Co₁₂P₇ (a = 904.3(1) pm, c = 363.9(1) pm) were carried out in the space group P6₃/m (Nr. 176), where the phosphorus atoms on the hexagonal axis are found on a Wyckoff site with a multiplicity of two but with an occupancy of one half. The discussion centres on this space group ambiguity in these and related structures. The near-neighbour environments of all compounds with Zr₂Fe₁₂P₇ type structure correspond to space group P.