CRYSTAL-STRUCTURE OF THE 1ST URANIUM OXYARSENIDE U2CU2AS3O

The crystal structure of U2Cu2As3O was determined from single-crystal X-ray data and refined to a residual of R = 0.037, R(w) = 0.034, for 4 43 reflections with I > sigma(I) and 22 variables. It is of a new type with tetragonal space group P4/nmm, Z = 2, and lattice parameters a = 3.9111(2) angstrom and c = 17.916(4) angstrom. A close relationship b etween the crystal structures Of U2Cu2As3O and UCuAs2 is discussed. U2 Cu2As3O appears to be the first known oxypnictide among uranium compou nds. However, in view of the results obtained for U2Cu2As3O, another u ranium compound, previously denoted as ''U4Cu4P7,'' is believed now to be U2Cu2P3O, closely related to the arsenide. (C) 1994 Academic Press , Inc.