The crystal structure of U2NiC3

The crystal structure of U2NiC3 was determined from single-crystal X-ray data and refined to a residual of R = 0.029 for 530 structure factors and 34 variable parameters. It is of a new type with orthorhombic symmetry, space group Pnma, a = 6.4145(3) A, b = 3.5457(2) A, c = 13.2315(7) A, V = 300.94 A3, and Z = 4 formula units per cell. The two crystallographically different uranium atoms have large coordination polyhedra formed by all three constituating components. The nickel atoms have no near nickel neighbour. One third of the Carbon atoms occupies octahedral voids formed by four uranium and two nickel atoms. The other two third form pairs (C-C-distance 1.43 A). One of the carbon atoms of each pair has approximately octahedral coordination with five uranium and one carbon neighbour, the other carbon atom has trigonal prismatic uranium coordination with two nickel and one carbon atom as additional neighbours outside the rectangular faces of the prism. The hydrolysis of U2NiC3 in hydrochloric acid yields mainly methane and ethane as well as some ethylene, propene and propane. (orig.)