THE CRYSTAL-STRUCTURE AND CHEMICAL-PROPERTIES OF U2AL3C4 AND STRUCTURE REFINEMENT OF AL4C3

A well crystallized sample of U2Al3C4 was obtained by melting the elemental components in a carbon crucible in a high frequency furnace. The crystal structure of this compound was determined from single-crystal diffractometer data of a twinned crystal: P6(3)mc, a = 342.2(1) pm. c = 2323.0(3) pm, Z = 2, R = 0.030 for 537 structure factors and 18 variable parameters. The structure can also be described in the higher symmetry space group P6(3)/mmc with one split aluminum position. It consists of close packed layers of uranium and aluminum atoms with carbon atoms at interstitial sites. The structure is closely related to that of Al4C3, which was refined from single-crystal X-ray data to a residual of R = 0.033 for 135 F-values and 11 variables. The hydrolysis of U2Al3C4 with diluted hydrochloric acid resulted in about 74 (wt-)% methane, 8% ethane and ethylene, and 18% saturated and unsaturated higher hydrocarbons.