Ein Orthoperrhenat mit flächenverknüpften ReO 6 -Oktaedern: Hochdrucksynthese und Kristallstruktur von K 3 NaRe 2 O 9 / An Orthoperrhenate with Face-Sharing ReO 6 Octahedra: High-Pressure Synthesis and Crystal Structure of K 3 NaRe 2 O 9

The title compound was prepared by high-pressure reaction of rhenium metal with technical grade (i.e., Na containing) KO 2 in a modified Belt-type apparatus (20 kbar, 1000 °C, 60 min, Au capsule). The amber-coloured crystals are very hygroscopic and decompose rapidly when exposed to air. K 3 NaRe 2 O 9 crystallizes hexagonally, space group P6 3 /mmc, with a = 6.012(1), c = 14.342(14) Å, c/a = 2.386 and Z = 2. The structure was refined to R = 0.031, R w = 0.023 for 422 independent, absorption-corrected reflections with l > σ (I). K 3 NaRe 2 O 9 is isostructural with 6H-BaTiO 3 , a perowskite variant, and contains Na and Re in octaedral coordination. Two ReO 6 octahedra are face-sharing, thus creating a Re 2 O 9 double octahedron with a Re-R e distance of 2.92 Å.