An EPR study of rhodium oxihydroxide

Rhodium oxihydroxide has been synthesized by means of hydrothermal synthesis at 1500 bars and 600°C in acidic media. Powder X-ray diffraction shows small variations in cell parameters which appear to be related to the oxidizing power of the reaction media. On the basis of EPR work such variations can be attributed to the presence of small amounts of either Rh(II) or Rh(IV). This last species had not been fully characterized before by EPR in oxide-like materials. The paramagnetic species seem to be noninteracting and randomly distributed in the Rh(III) sites. These results can be understood on the basis of two different kinds of nonstoichiometry for rhodium oxihydroxide: either proton or hydroxyl ion defects.