Syntheses, crystal structures, transport properties, and theoretical studies of five members of the MAn₂Q₅ Family: SrU₂S₅, BaU₂Se₅, PbU₂S₅, BaTh₂S₅, and BaU₂Te₅

Five compounds of the MAn₂Q₅ family, namely, SrU₂S₅, BaU₂Se₅, PbU₂S₅, BaTh₂S₅, and BaU₂Te₅, have been synthesized by higherature solid-state reactions. The crystal structures of these compounds were determined by single-crystal X-ray diffraction studies. SrU₂S₅, BaU₂Se₅, PbU₂S₅, and BaTh₂S₅ crystallize in the PbU₂Se₅ structure type in space group C2h₅-P2₁/c of the monoclinic system, whereas BaU₂Te₅ adopts the (NH₄)Pb₂Br₅ structure type in space group D4h₁₈-I4/mcm of the tetragonal system. There are no Q-Q bonds in these structures, so the formulas charge balance as M²⁺(An⁴⁺)₂(Q^2-)₅. The An atoms in the monoclinic structure are seven- or eight-coordinated by Q atoms; the U atoms in the tetragonal structure are eight-coordinated. The M atoms in the monoclinic structure are coordinated to either eight or nine Q atoms, depending on the monoclinic angle; the M atoms in the tetragonal structure are 10-coordinated. Resistivity studies on single crystals of SrU₂S₅, BaU₂Se₅, and PbU₂S₅ show metallic behavior with resistivities of 0.24, 10, and 3.3 m·cm, respectively, at 298 K. Spin-polarized density functional theory in the generalized gradient approximation applied to the four U compounds suggests that they are ferromagnetic. In each compound, the density of states of one spin channel is found to be finite at the Fermi level, whereas there is a gap in the density of states of the other spin channel; this is characteristic of a half-metal.