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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 D3d(6)–R3c. Both structures feature infinite ∞(1)[MUS6(6–)] chains along c that are separated by Ba atoms. The ∞(1)[FeUS6(6–)] chains are formed by the face-sharing of US6 trigonal prisms with FeS6 octahedra; in contrast, the ∞(1)[AgUS6(6–)] chains are formed by the face-sharing of US6 octahedra with AgS6 trigonal prisms. The Ba3FeUS6 compound charge balances with 3 Ba(2+), 1 Fe(2+), 1 U4+, and 6 S(2–), whereas Ba3AgUS6 charge balances with 3 Ba(2+), 1 Ag(1+), 1 U(5+), and 6 S(2–). 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.

a b s t r a c tBlack crystals of Ba 9 Ag 10 U 4 S 24 have been made by direct combination of BaS, Ag, U, and S at 1273 K. This compound crystallizes in a new structure type in the space group C 10 4v À I4cm of the tetragonal system with four formula units in a cell with lattice constants a¼13.9189(6) Å and c¼23.7641(11) Å (V¼4604(5) Å 3 ). Multiphoton Luminescence Spectroscopy measurements are consistent with the noncentrosymmetric nature of the structure. In the structure each U atom is octahedrally coordinated by six S atoms, whereas three of the five crystallographically independent Ag atoms are tetrahedrally coordinated to four S atoms, another has a seesaw coordination to four S atoms, and the last has a triangular coordination to three S atoms. The overall structure consists of the three-dimensional stacking of the US 6 , AgS 4 , and AgS 3 polyhedra to leave channels in which Ba atoms reside. Based on the values of the U-S interatomic distances, the compound Ba 9 Ag 10 U 4 S 24 contains U 5 þ and charge balance is achieved with the formal oxidation states of 9 Ba 2 þ , 10 Ag 1 þ , 4 U 5 þ and 24 S 2À . DFT calculations predict an antiferromagnetic ground state and a band gap of 2.1 eV. Resistivity measurements indicate that the compound is a semiconductor with a complex activation mechanism and activation energies ranging from 0.03(1) eV to 0.08(1) eV.

Two new compounds, Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5, have been synthesized in fused-silica tubes by the direct combinations of V or Fe with U, BaS, and S at 1223 K. The compound Ba7UV2S12.5O0.5 crystallizes at 100 K in the Cs7Cd3Br17 structure type in space group D4h(18)–I4/mcm of the tetragonal system. The compound Ba7UFe2S12.5O0.5 crystallizes at 100 K in space group D4h(5)–P4/mbm of the tetragonal system. The structures are very similar with V/S or Fe/S networks in which Ba atoms reside as well as channels large enough to accommodate additional Ba atoms and infinite linear US5O chains. Each U atom is octahedrally coordinated to four equatorial S atoms, one axial S atom, and one axial O atom. The Fe/S network contains a S–S single bond, whereas the V/S network does not. The result is that the Fe3+ compound charge balances with 7 Ba2+, U4+, 2 Fe3+, 10.5 S2–, S2(2–), and 0.5 O2–, whereas the V4+ compound charge balances with 7 Ba2+, U4+, 2 V4+, 12.5 S2–, and 0.5 O2–. Other differences between these two compounds have been characterized by Raman spectroscopy and resistivity measurements. DFT calculations have provided insight into the nature of their bonding. The overall structural motif of Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5 offers a remarkable flexibility in terms of the oxidation state of the incorporated transition metal.

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