The phosphides U₆Fe₃₀P₁₉ and U ₆Co₃₀P₁₉ with the Yb₆Co ₃₀P₁₉ structure type

Powders of U₆Fe₃₀P₁₉ and U ₆Co₃₀P₁₉ were synthesized through the use of tin fluxes. Examination of these powders at 298 K by the Guinier technique led to lattice parameters in the hexagonal system for U₆Fe ₃₀P₁₉ of a = 14.762(2) Å, c = 3.6315(4) Å, c/a = 0.2460, V = 685.3 ų and for U₆Co ₃₀P₁₉ of a = 14.722(3) Å, c = 3.6355(6) Å, c/a = 0.2469, V = 682.4 ų. Single crystals of U ₆Fe₃₀P₁₉ were synthesized and its structure was determined. U₆Fe₃₀P₁₉ crystallizes in the space group C¹,_3h - P$\bar{6}$ of the hexagonal system in the Yb₆Co₃₀P₁₉ structure type with one formula unit in a cell of dimensions determined at 100 K of a = 14.7206(4) Å, c = 3.6243(1) Å, c/a = 0.2462, V = 680.15(4) ų. The asymmetric unit of U₆Fe₃₀P ₁₉ comprises two U, ten Fe, and seven different P atoms. Each U atom is situated in a trigonal prism of six P atoms; each Fe atom is coordinated either by a tetrahedron or a square pyramid of P atoms. The distances are all less than 2.9 Å. In addition, the structure contains numerous Fe-Fe bonds covering the range from 2.55 to 2.71 Å. The proper space group of the Yb₆Co₃₀P₁₉ structure type is discussed.