The electrochemistry of Rh(NH3),0HZ+ has been studied in a buffered ammoniacal solution. The polarographic reduction wave at the dropping mercury electrode had equal to -1.10 V (vs. saturated calomel electrode) in a 0.10 M N H , -0.10 MNH,C10, electrolyte, and gross Hg cathode electrolysis at -1.19 V produced a stable Rh(NH3),Hz+ hydride species. Both reductions were found to take place through a Rh(I) intermediate.The reaction of the Rh(NH3),HZ+ with molecular OZ in the ammoniacal electrolyte was also studied. The product was demonstrated to be a stable Rh(NH3)4(0H)(OZH)+ hydroperoxo species.

The polarography and coulometry of Rh(II1) has been studied in an aqueous pyridine -pyridinium chloride -sodium chloride electrolyte at pH 5.30 and ionic strength 0.30 M at 25.0 "C. Two distinct types of polarographic behavior were noted as the total Py concentration was varied between 0.05 and 0.45 M, a "normal" wave with E l I 2 of -0.43 V VS. a standard calomel electrode, and a second catalytic wave which under some conditions masked the normal wave.For both types of behavior, controlled potential electrolysis gave a well-defined two electron reduction but there was a definite H + consumption in the electrolyses. It is postulated that hydride species are involved in the reduction according to the scheme Rh(1II) + 2e -> Rh(I) "normal", diffusion controlled wave at dropping mercury electrode "enhanced" wave