Sr[ReO4]2: The First Single Crystals of an Anhydrous Alkaline-Earth Metal Meta-Perrhenate

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 O^2– 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.