Solid-State Structures of XeO3

The solid-state structure of xenon trioxide, XeO3, was reinvestigated by low-temperature single-crystal X-ray diffraction and shown to exhibit polymorphism that is dependent on the crystallization conditions. The previously reported α-phase (orthorhombic, P212121) only forms upon evaporation of aqueous HF solutions of XeO3. In contrast, two new phases, β-XeO3 (rhombohedral, R3) and γ-XeO3 (rhombohedral, R3c), have been obtained by slow evaporation of aqueous solutions of XeO3. The extended structures of all three phases result from XeO---Xe bridge interactions among XeO3 molecules that arise from the amphoteric donor–acceptor nature of XeO3. The Xe atom of the trigonal-pyramidal XeO3 unit has three Xe---O secondary bonding interactions. The orthorhombic α-XeO3 displays the greatest degree of variation among the contact distances and has a significantly higher density than the rhombohedral phases. The ambient-temperature Raman spectra of solid α- and γ-XeO3 have also been obtained and assigned for the first time.