Browsing by Author "Conrad, Maurice"

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    On the thermal dimorphy of the strontium perrhenate Sr[ReO4]2
    (2024) Conrad, Maurice; Bette, Sebastian; Dinnebier, Robert E.; Schleid, Thomas
    Hygroscopic single crystals of a new hexagonal high‐temperature modification of Sr[ReO4]2 were prepared from a melt of Sr[ReO4]2 ⋅ H2O and SrCl2 ⋅ 6 H2O. The structure analysis of the obtained crystals by X‐ray diffraction revealed that the title compound crystallizes in the ThCd[MoO4]3‐type structure with the hexagonal space group P63/m and the lattice parameters a=1023.81(7) pm and c=646.92(4) pm (c/a=0.632) for Z=2 in its quenchable high‐temperature form. Two crystallographically independent Sr2+ cations are coordinated by oxygen atoms forming either octahedra or tricapped trigonal prisms, whereas the Re7+ cations are found in the centers of discrete tetrahedral meta‐perrhenate units [ReO4]-. Temperature‐dependent in‐situ PXRD studies of dry powder samples of Sr[ReO4]2 exhibited its thermal dimorphy with a phase‐transition temperature at 500-550 °C from literature‐known m‐Sr[ReO4]2 into the newly discovered h‐Sr[ReO4]2 (hexagonal).
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    Single crystals of CaNa[ReO4]3 : serendipitous formation and systematic characterization
    (2019) Conrad, Maurice; Schleid, Thomas
    In an attempt to crystallize Ce[ReO4]4·xH2O from aqueous solutions of equimolar amounts of Ce[SO4]2 and Ba[ReO4]2 via salt‐metathesis the serendipitous formation of colorless, transparent, rod‐shaped single crystals of CaNa[ReO4]3 was observed as a result of calcium and sodium impurities within the improperly deionized water used. Structure analysis by X‐ray diffraction lead to the conclusion that the title compound crystallizes in the ThCd[MoO4]3 structure type with the hexagonal space group P63/m and the lattice parameters a = 991.74(6) pm, c = 636.53(4) pm, c/a = 0.642 for Z = 2. The crystal structure contains purely oxygen surrounded and crystallographically unique cations, namely Ca2+ in tricapped trigonal prismatic (d(Ca-O) = 6 × 249 pm + 3 × 254 pm), Na+ in octahedral (d(Na-O) = 6 × 241 pm), and Re7+ in tetrahedral coordination (d(Re-O) = 171-173 pm). Furthermore, it was possible to yield an almost phase‐pure microcrystalline powder of the title compound from a melt of equimolar amounts of Na[ReO4] and Ca[ReO4]2 stemming from aquatically obtained precursors.
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    Sr[ReO4]2 : the first single crystals of an anhydrous alkaline‐earth metal meta‐perrhenate
    (2020) Conrad, Maurice; Russ, Philip L.; Schleid, Thomas
    Colorless single crystals of Sr[ReO4]2 were obtained from halide melts at 1123 K in open corundum crucibles. X‐ray diffraction revealed that Sr[ReO4]2 crystallizes in the monoclinic space group P21/n with the lattice parameters a = 627.31(4) pm, b = 1004.56(7) pm, c = 1271.25(9) pm and β = 97.118(3)° for Z = 4. The crystal structure contains a unique Sr2+‐cation site surrounded by eight crystallographically different oxygen atoms forming distorted bicapped trigonal prisms. All corners of these [SrO8]14- polyhedra (d(Sr-O) = 259-268 pm) are shared with tetrahedral meta‐perrhenate units [ReO4]- (d(Re-O) = 166-173 pm) formed from two crystallographically different Re7+ cations surrounded by four O2- anions each, building up the three‐dimensional mosaic‐like structure of Sr[ReO4]2. Single‐crystal Raman data confirm the presence of two different kinds of symmetry‐free meta‐perrhenate units [ReO4]- and match well with results known from literature.