Xenon Hexafluoride: Structural Crystallography of Tetrameric Phases

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Science  05 Feb 1971:
Vol. 171, Issue 3970, pp. 485-487
DOI: 10.1126/science.171.3970.485


Three crystalline phases of xenon hexafluoride are based on tetrameric association of XeF5+ and F- ions into eight-membered rings. Phase I (monoclinic, 8 XeF6 units per cell) transforms at ∼ 10°C to phase II (orthorhombic, 16 XeF6 units per cell), which in turn transforms at ∼ -25°C to phase 111 (monoclinic, 64 XeF6 units per doubly primitive cell). The transformation from phase I to phase II requires gross reorientation of half of the tetramers in the structure. The transformation from phase II to phase III involves only an ordering of right-handed and left-handed configurations.