Syntheses, Crystal Structures, Transport Properties, and Theoretical Studies of Five Members of the MAn2Q5 Family: SrU2S5, BaU2Se5, PbU2S5, BaTh2S5, and BaU2Te5

Overview of the crystal chemistry of the actinide chalcogenides: incorporation of the alkaline-earth elements

This review focuses on the results of exploratory syntheses of alkaline-earth-metal actinide chalcogenides Ak–An–Q (Ak = Ba, Sr; An = Th, U; Q = S, Se, and Te). About thirty new compounds and eleven new structure types are described.

Three new quaternary actinide chalcogenides Ba2TiUTe7, Ba2CrUTe7, and Ba2CrThTe7: syntheses, crystal structures, transport properties, and theoretical studies

The three new quaternary actinide chalcogenides Ba2TiUTe7, Ba2CrUTe7, and Ba2CrThTe7 have been synthesized. From single-crystal X-ray diffraction studies these isostructural compounds are found to crystallize in a new structure type in space group D2h16–Pnma of the orthorhombic system. The structure features ∞1[MAnTe74–] strips (M = Cr or Ti; An = Th or U) that propagate in the b-direction and are separated by Ba cations. An atoms are coordinated to eight Te atoms in a bicapped trigonal-prismatic geometry while M atoms are octahedrally coordinated to six Te atoms. Sharing of the AnTe8 and MTe6 polyhedra forms ∞1[MAnTe74–] strips. The presence of the infinite linear Te–Te–Te chains in these compounds makes assignment of oxidation states arbitrary. Resistivity measurements and DFT calculations provide further insight into the properties of these compounds.

Synthesis, crystal structure, resistivity, magnetic, and theoretical study of ScUS3

Single crystals of ScUS3 were synthesized in high yield in a single step at 1173 K. ScUS3 crystallizes in the FeUS3 structure type in the space group D2h(17)–Cmcm of the orthorhombic system with four formula units in a cell of dimensions a = 3.7500(8) Å, b = 12.110(2) Å, and c = 9.180(2) Å. Its structure consists of edge- and corner-sharing ScS6 octahedra that form two-dimensional layers. U atoms between layers are connected to eight S atoms in a bicapped trigonal-prismatic fashion. ScUS3 can be easily charge-balanced as Sc(3+)U(3+)(S(2–))3 as there are no S–S single bonds present in the crystal structure. High temperature-dependent resistivity measurements on a single crystal of ScUS3 show semiconducting behavior with an activation energy of 0.09(1) eV. A magnetic study on powdered single crystals of ScUS3 reveals an antiferromagnetic transition at 198 K followed by a ferromagnetic transition at 75 K. The weak ferromagnetic behavior at low temperature may originate from canted antiferromagnetic spins. A density functional theory (DFT) calculation predicts ScUS3 to be ferromagnetic and either a very poor metal or a semiconductor with a very small gap.

Syntheses, crystal structures, resistivity studies, and electronic properties of three new barium actinide tellurides: BaThTe4, BaUTe4, and BaUTe6

The three new solid-state compounds BaThTe4, BaUTe4, and BaUTe6 have been synthesized and characterized. BaThTe4 and BaUTe4 are isostructural. The structure consists of infinite ∞(2)[AnTe4(2–)] layers separated by Ba(2+) ions. Each An (An = Th, U) atom is coordinated to eight Te atoms in a bicapped trigonal-prismatic arrangement. Te atoms are connected to each other to form linear infinite chains. These Te–Te interactions are longer than that of a Te–Te single bond. However, this structure also possesses Te–Te single bonds. Charge balance in the formula BaAnTe4 may be achieved with [Ba(2+)]2[(An(4+))2(Te(2–))2(Te2(2–))(Te2(3–))2](4–). The structure of BaUTe6 features one-dimensional anionic ∞(1)[UTe6(2–)] chains that are separated by Ba(2+) ions. There are three Te–Te single bonds around each U atom. The anion in this structure can thus be described as [U(4+)(Te2(2–))3](2–). Resistivity measurements on single crystals of BaThTe4 and BaUTe6 show semiconducting behavior. DFT calculations indicate finite band gaps for BaThTe4 and for BaUTe6, whereas BaUTe4 has a vanishing density of states at the Fermi level.