Abstract
Fine, whisker-like crystals of Rb 2Fe 5F 17 have been obtained from solid state stoichiometric mixtures of RbF and FeF 3. A structural model has been determined from single crystal diffractometer data in the Fmmm orthorhombic space group : a = 14.887(2) A ̊ , b = 25.814(3) A ̊ , c = 7.560(1) A ̊ ; z = 8; ϱ exp. = 3.529 g cm −3; ϱ calc.=3.535 g cm −3; λ Co Ka =1.7903 A ̊ ; R = 0.068; R ω = 0.096 for 175 reflections with I σ( I) > 6 . The structure has been compared with that of HTB. Rb 2Fe 5F 17 exhibits layers of (Fe 5F 17) 2n− n composition containing FeF 6 corned-shared octahedra forming tunnels of hexagonal and triangular sections. Rubidium atoms are located between the layers and within the hexagonal tunnels with statistical occupancy. The structure has been roughly confirmed by TEM. The observed lowering in symmetry from Fmmm may be explained by partial ordering of rubidium and by possible bridging of (Fe 5F 17) sheets by FeF 6 octahedra.
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