The crystal structure of URu3B2

The crystal structure of URu3B2 has been determined by single crystal X-ray analysis. URu3B2 crystallizes in the trigonal space group Panti 3 (C3sub(i)1) with hexagonal lattice a = 1.09531(14), c = 0.59353(8) nm, Z = 8. Intensity measurements were obtained from a fourcircle diffractometer. The structure was solved by Patterson methods and refined by full matrix least squares calculation. The final R-value, R = Σ vertical stroke ΔF vertical stroke /Σ vertical stroke F0 vertical stroke, is 0.052 for an asymmetric set of 962 independent reflections ( F0 > 2sigma (F0)). The crystal structure is a twofold superstructure (distortion-derivative) of the CeCo3B2-type cell (a = 2a', c = 2c') and thus closely related to the CaCu5 type structure. The coordination numbers of U are 2 U + 12 Ru + (6 B) and those of Ru atoms 4 U + 6 Ru + 4 B. The isolated boron atoms have tetrakaidekahedral metal coordination 6 Ru + 3 U; no boron-boron contacts occur. The structural chemistry of (Th, U, RE)Ru3B2 phases is discussed. (orig.)