Syntheses, Structures, and Electronic Properties of Ba3FeUS6 and Ba3AgUS6

The compounds Ba3FeUS6 and Ba3AgUS6 have been synthesized by the reactions of BaS, U, S, and M (= Fe or Ag) at 1223 K. These two isostructural compounds crystallize in the K4CdCl6 structure type in the trigonal system in space group D3d6–R3̅c. Both structures feature infinite ∞1[M­US66–] chains along c that are separated by Ba atoms. The ∞1[Fe­US66–] chains are formed by the face-sharing of US6 trigonal prisms with FeS6 octahedra; in contrast, the ∞1[Ag­US66–] chains are formed by the face-sharing of US6 octahedra with AgS6 trigonal prisms. The Ba3FeUS6 compound charge balances with 3 Ba2+, 1 Fe2+, 1 U4+, and 6 S2–, whereas Ba3AgUS6 charge balances with 3 Ba2+, 1 Ag1+, 1 U5+, and 6 S2–. This structure offers a remarkable flexibility in terms of the oxidation state of the incorporated uranium depending on the oxidation state of the d-block metal. DFT calculations performed with the HSE functional have led to band gaps of 2.3 and 2.2 eV for Ba3FeUS6 and Ba3AgUS6, respectively. From resistivity measurements, the Arrhenius activation energies are 0.12(1) and 0.43(1) eV for Ba3FeUS6 and Ba3AgUS6, respectively.