Rb4O6 studied by elastic and inelastic neutron scattering

The black rubidium oxide Rb4O6 has been described to be a mixed peroxide-hyperoxide Rb-4(O-2(2-))(O-2(-))(2) in the literature. Previous X-ray diffraction studies on powders and single crystals, however, revealed that Rb4O6 crystallises like cubic Pu2C3 (space group I3d), and has only one crystallographically independent: position for a dumbbell-shaped molecular ion. Elastic neutron scattering now shows that this structure is stable down to 5 K, and no reduction of symmetry nor ordering of the differently sized yet indistinguishable dioxygen anions takes place. The presence of the peroxide and hyperoxide anions in Rb4O6 at 4 K is proved by inelastic neutron scattering, resulting in two absorptions at 750 cm(-1) and 1 130 cm-l, which correspond to the stretching vibrations of O-2(2-) and O-2(-). (C) 1999 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.