Actinoid transition metal phosphides An_2T_(12)P _7 (An = Th, U; T = Fe, Co, Ni) and arsenides An_2T _(12)As_7 (An = Th, U; T = Co, Ni) with Zr_2Fe _(12)P_7 type structure

摘要

The preparation and the lattice parameters for the ten title compounds with Zr_2Fe_(12)P_7 type structure are reported; six of them for the first time. The crystal structures of the phosphides Th _2Fe_(12)P_7 (a = 917.3(1) pm, c = 372.2(1) pm), U_2Fe_(12)P_7 (a = 908.7(2) pm, c = 364.1(1) pm) and U_2Ni_(12)As_7 (a = 935.9(1) pm, c = 383.5(1) pm) were refined in the space group P6 (Nr. 174), where all atomic positions are fully occupied. In contrast, the structure refinements of the phosphides Th _2Co_(12)P_7 (a = 912.8(1) pm, c = 370.5(2) pm) and U_2Co_(12)P_7 (a = 904.3(1) pm, c = 363.9(1) pm) were carried out in the space group P6_3/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 Zr_2Fe_(12)P_7 type structure correspond to space group P6.