Low-temperature fluorination of ruthenium and osmium di- and tetra-oxides

Abstract

The fluorination of ruthenium dioxide, RuO 2, and osmium di- and tetra-oxides, OsO 2 and OSO 4, has been studied at ambient temperature using fluorinating agents of variable strength such as chlorine trifluoride ClF 3, bromine pentafluoride BrF 5 or krypton difluoride KrF 2. The results of this study and those previously obtained on the fluorination of ruthenium and osmium tetroxides (RuO 4, OSO 4) are compared and discussed. The reaction of RuO 2 with KrF 2 in HF solution leads to the ruthenium(V) dioxygenyl salt, O 2 +RuF 6 −, and that of OsO 2 to osmium oxide pentafluoride, OsOF 5. This oxide fluoride also results from the reaction of OsO 2 or OsO 4 with liquid ClF 3. However, osmium trioxide difluoride, OsO 3F 2, and small quantities of osmium dioxide tetrafluoride, OsO 2F 4, are formed at intermediate stages of the fluorination of OsO 4 by ClF 3. A slow reaction takes place between liquid BrF 5 and OsO 4 to yield OsO 3F 2 as the sole osmium derivative. A large excess of KrF 2 or its derivative cation KrF + in HF solution leaves OsOF 5 unreacted. In contrast to the strength of the metal-oxygen bonds generally observed for the oxide fluorides of osmium in high oxidation states, the weakness of the corresponding Ru-O bonds is the rule. The differences between the fluorination pathways of the oxides of ruthenium and those of osmium are thus explained.