Positional Flexibility: Syntheses and Characterization of Six Uranium Chalcogenides Related to the 2H Hexagonal Perovskite Family

Six new uranium chalcogenides, Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, Ba3MnUS6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, related to the 2H hexagonal perovskite family have
been synthesized by solid-state methods at 1173 K. These isostructural
compounds crystallize in the K4CdCl6 structure
type in space group D3d6–R3̅c of the trigonal system with six formula
units per cell. This structure type is remarkably flexible. The structures
of Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 consist of infinite ∞1[MUQ66–] chains (M = Fe or Mn; Q = S or Se) oriented
along the c axis that are separated by Ba atoms.
These chains are composed of alternating M-centered octahedra and
U-centered trigonal prisms sharing triangular faces; in contrast,
in the structures of Ba4USe6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, there are U-centered octahedra alternating with Ba-,
Rb-, or K-centered trigonal prisms. Moreover, the Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 compounds contain U4+, whereas Ba3.3Rb0.7US6 and
Ba3.2K0.8US6 are mixed U4+/5+ compounds. Resistivity and μ-Raman spectroscopic measurements
and DFT calculations provide additional insight into these interesting
subtle structural variations.