The compound La2U2Se9 was obtained in high yield from the stoichiometric reaction of the elements in an Sb 2Se3 flux at 1123 K. The compound, which crystallizes in a new structure type in space group Pmma of the orthorhombic system, has a three-dimensional structure with alternating U/Se and La/Se layers attached via three independent, infinite polyselenide chains. The U atom has a monocapped square antiprismatlc coordination of Se atoms, whereas one La atom is bicapped square prismatic and the other La atom is trigonal prismatic. La 2U2Se9 displays an antiferromagnetic transition at TN = 5 K; above 50 K, the paramagnetic behavior can be fit to the Curie-Weiss law, yielding a μeff of 3.10(1) μB/U. The low-temperature specific heat of La2U2Se9 exhibits no anomalous behavior near the Néel temperature that might indicate long-range magnetic ordering or a phase transition. X-ray absorption near-edge structure (XANES) spectra have confirmed the assignment of formal oxidation states of +III for lanthanum and +IV for uranium in La 2U2Se9.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry