Lithium-uranium-nitrides: LiUN2 and Li2UN2

The synthesis of LiUN2 started with a mixture of Li3N with UH3 reacted under N-2 at 900 degreesC within 3 d. The compound crystallizes (X-ray and neutron diffraction powder data) tetragonal in the space group I4(1)/amd with Z = 4 and a = 4.3965 (2) A, c = 11.059 (4) Angstrom. The Structure is related to the anatase type (TiO2 UN2) with filled up octahedral sites by Li. The compound is a paramagnetic semiconductor. Reactions of mixtures of Li3N and UH3 (3 : 1) at 600 degreesC result as the main product in a Li2UN2 just known for a long time. In contrary to the earlier investigations our product does not crystallize in the space group P(3) over bar with Z = 3 but in P(3) over bar m I with Z = 1. Mixtures in a molar ratio of 5 : I reacted at 500 degreesC give a product that crystallizes cubic with a = 4.890 (1) Angstrom. Its lattice constant resembles that of UN. Reactions carried out with high molar ratios of educts from 5 : I to 10 : I and temperatures greater than or equal to 800 degreesC give Guinier diagrams indicating a further phase in the system Li/U/N with a somewhat complicated structure as to the number of X-ray lines.