Ba2Mn2O4Cu0.9S:: A layered oxysulfide with a new perovskite-related manganese oxide fragment

The oxysulfides Ba2Mn2O4Cu0.9S and Ba1.3Sr0.7Mn2O4CuS are reported. The compounds crystallize in space group P4/nmm with 2 formula units in the unit cell and lattice parameters a = 3.9916(1) angstrom and c = 19.5628(5) angstrom for a refined composition of Ba2Mn2O4CU0.89(1)S and a = 3.9595(1) angstrom and c = 19.2227(3) angstrom for Ba1.32(3)Sr0.68(4)Mn2O4Cu0.98(2)S determined, respectively, from powder neutron and X-ray single-crystal diffraction measurements. The structure consists of alkaline earth Manganite slabs composed of MnO5 square-based pyramids sharing edges and vertexes, which are separated by CuS antifluorite-type puckered layers. The central part of the alkaline earth manganite slab is composed of MnO5 square-based pyramidal units sharing all four of their basal edges with neighboring units in the basal plane and sharing their apical vertices with those of square-based MnO5 pyramids in the outer part of the alkaline earth manganite slab. This is similar to a structural fragment in the as-yet-unrealized strontium iron oxide Sr4Fe6O12, which is the oxide-poor relative of the anion-conducting Sr4Fe6O13 +/-delta phases. The intrinsic copper deficiency in semiconducting Ba2Mn2O4Cu0.9S suggests a mean manganese oxidation state of +2.55. The results of magnetic susceptibility measurements and low-temperature neutron diffraction results suggest that some moments participate in long-range antiferromagnetic order, whereas others give rise to spin-glass-like behavior.