Preparation and crystal structure of U₃Fe₂C₅: An original uranium–iron carbide

Highlights: • The U₃Fe₂C₅ uranium ternary carbide was prepared. • The crystal structure of U₃Fe₂C₅ was successfully solved from XRD data by direct methods. • U₃Fe₂C₅ crystallizes in a new structure type. • Pairs and isolated carbon atoms exist in the U₃Fe₂C₅ structure. • The structure of U₃Fe₂C₅ is closely related to UC and UFeC₂. - Abstract: The U₃Fe₂C₅ compound was prepared from the elements by arc-melting, followed by an heat-treatment in an induction furnace, at 1250 °C for 1 h and 1300 °C for 2 h. The crystal structure of this phase was determined by direct methods from single crystal X-ray diffraction data. U₃Fe₂C₅ crystallizes in an original tetragonal crystal structure, with space group I4/mmm, a = 3.4980(3) Å and c = 19.8380(15) Å as lattice constants and two formula units per cell. This new type structure is characterized by the simultaneous presence of isolated and pairs of carbon atoms, the interatomic distances in the pairs being similar to a typical carbon–carbon double bond length found in a molecule. U₃Fe₂C₅ is closely related to UC and UFeC₂, and can be seen as build from two (distorted) UFeC₂ unit cells and a UC layer