Tri-µ-bromo-bis[tribromoruthenate(III)] salts: a synthetic, structural, spectroscopic, and electrochemical study

The salts A3[Ru2Br9][A = Rb, Cs, or 1-ethyl-3-methylimidazolium (emim)] have been prepared, and studied by electronic absorption spectroscopy and electrochemistry in both conventional solvents and a basic room-temperature ionic liquid, AlBr3–[emim]Br: the mixed-valence complex [RU2Br9]4– was generated on the electrochemical time-scale in the latter medium. The caesium and rubidium salts were characterized by powder X-ray diffraction, and the structure of the [emim]+ salt was determined by single-crystal X-ray diffraction: the anion is an almost idealized confacial bioctahedron, but there is a significant metal–metal interaction [r(RuRu)= 0.288 0(3) nm]. Literature reports that A4[Ru2OBr10](A = Rb or Cs) had been prepared and characterized are shown to be erroneous: the products are mixtures of A3[Ru2Br9] and ABr.