La₂U₂Se₉: An Ordered Lanthanide/Actinide Chalcogenide with a Novel Structure Type

Abstract

The compound La(2)U(2)Se(9) was obtained in high yield from the stoichiometric reaction of the elements in an Sb(2)Se(3) 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 antiprismatic coordination of Se atoms, whereas one La atom is bicapped square prismatic and the other La atom is trigonal prismatic. La(2)U(2)Se(9) displays an antiferromagnetic transition at T(N) = 5 K; above 50 K, the paramagnetic behavior can be fit to the Curie-Weiss law, yielding a mu(eff) of 3.10(1) mu(B)/U. The low-temperature specific heat of La(2)U(2)Se(9) exhibits no anomalous behavior near the Neel 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(2)U(2)Se(9).

Highly Luminescent and Stable Hydroxypyridinonate Complexes: A Step Towards New Curium Decontamination Strategies

“…Although the octadentate ligand coordinates through eight oxygen donor atoms (as previously demonstrated by Xray diffraction characterization of 1,2-HOPO and Me-3,2-HOPO metal complexes [18,19] ), one additional water molecule is interacting in the primary coordination sphere, which may lead to either a monocapped square antiprismatic or a trigonal prismatic structure, as known for Ln III and An III . [26,27] For the 5-LIO(Me-3,2-HOPO) complex, the parameter q was calculated as 2.5 at pH 7.4 and 2.3 at pH 8.9 (t obs = 206 ms; see the Supporting Information, Figure S2), leading to a ten-coordinate complex. The coordination number is higher for the complex formed with 5-LIO(Me-3,2-HOPO), in comparison with 3,4,3-LI(1,2-HOPO), as the 2:1 ligand/metal ratio required to fully coordinate the metal with this tetradentate ligand results in higher flexibility of the coordination sphere and less steric hindrance around the metal core, facilitating access of two water molecules.…”

Synthesis, structure, and electrical resistivity of Cs3U18Se38

“…Atom U2 (site symmetry ..m) is in a monocapped square antiprism ( Fig. 3(b)), which is also found in La 2 U 2 Se 9 [21]. Atom U3 (site symmetry .2.)…”

“…These elements are likely forming P 2 Se 5 or As 2 Se 3 in situ. Pnicogen chalcogenides have been used to synthesize other uranium chalcogenides, such as LaU 2 Se 9 [21]. Attempts at using Sb or Sb 2 Se 3 failed, however, suggesting the size of the pnicogen element plays a role in the crystallization of Cs 3 U 18 Se 38 .…”

Specific Induced Circular Dichroism and Enhanced B to Z Transitions of Duplexes Stabilized by Chromophore‐Linked Alkynylnucleoside Residues

“…Due to their similar ionic radii, most extended solid‐state chalcogenides containing both a lanthanide and an early actinide are either modifications of known binary Ln or An phases or exhibit Ln/An disorder. In contrast, La 2 U 2 Se 9 94 represents a novel structure type with alternating U/Se and La/Se layers connected through three independent infinite selenium chains. Two of these chains are depicted in Figure 17 for the bicapped LaSe 8 trigonal prisms of one of the two independent lanthanide atoms.…”

“… Infinite polyselenide chains in the coordination sphere of bicapped LaSe 8 trigonal prisms (shaded)in La 2 U 2 Se 9 94…”