CHARACTERIZATION OF 3 ACTIVE RHODIUM(III) HYDROXIDES

Pure solutions of [Rh(H2O)6](3+) dimer [Rh-2(mu-OH)(2)(H2O)(8)](4+) an d trimer [Rh-3(mu-OH)(4)(H2O)(10)](5+) have been converted into their respective 'active' hydroxides by dropwise addition to an imidazole so lution. These 'active' hydroxides have been analysed by a variety of t echniques including rhodium determination, infrared spectroscopy, ther mal analysis and powder X-ray diffraction. Purity determinations using ion-exchange chromatography showed that the three hydroxides consist primarily of the neutral forms of the starting aqua ion (>96%) with sm all amounts of species with higher nuclearity. Rhodium analysis and th ermogravimetric measurements confirmed the composition of these hydrox ides to be Rh(OH)(3)(H2O)(3).H2O, Rh-2(mu-OH)(2)(OH)(4)(H2O)(4) and Rh -3(mu-OH)(4)(OH)(5) (H2O)(5).5H(2)O. A scheme for the thermal decompos ition of each of the hydroxides has been proposed on the basis of the t.g. and d.t.a. data and the knowledge that the final product alpha-Rh 2O3 Beating of the hydroxides in air resulted in oxidation of Ph(III) to Rh-IV (temperature 250-300 degrees C) forming RhO2 which on further heating decomposed to alpha-Rh2O3 and dioxygen.