Reductive polarograms, initially obtained by Rosseinsky and Kite 1 , showed four waves, which could have indicated a separate wave for the reduction of each platinum oxidation state in the process (IV) -~ (0). It was recognised 1 that the final wave at -1.8 V (vs. 0.5 M Na2 SO4/Hg2 SO4/Hg) could have been a proton-reduction wave catalysed by (a) Pt species, and the present measurements at varying pH were made to check this point. Furthermore, the second wave could 2 ,3 be due to the presence of halide, so this was also checked. Finally, since the exchange of the three H20 molecules is virtually quenched at 0 ยฐC, relative to a comparative lability at 25 ยฐC, polarograms were obtained at 0 ยฐC to establish whether possible bridging by the SO42-present might be prevented, so potentially producing a markedly different polarogram.
Rigorous exclusion of halide in new samples was indeed found to remove the second wave at -1.35 V. Then, introduction of 1.2 x 10 -a MC1-to the 5 x 10 -3 M MeaPt + restored this wave ~ , so establishing one possible origin: either adventitious chloride, or some C1-from the hexachloroplatinate starting material, present in the original sample.
The height of the Final wave was found to be markedly pH dependent: 16.5/aA at pH 3".75, 7.6 at 4.00, 2.8 at 5.4, and 1.6 at 6.6, in acetate buffers. (These figures are more illustrative than exact, because of marked maxima especially at the lower pH values.) A complex [H +] dependence is evident, confirming that discharge of this ion is at least in part responsible for the final wave at -1.8 V.
Finally, little effect on cooling the system to 0 ยฐC, other than a slight (~ 0.02 V) shift to more negative potentials, is observed for the two surviving Pt-reduction waves, indicating either nil SO42-bridging, or roughly the same magnitude of effect at both temperatures.
We are indebted to Dr. Hall for discussion, and hope that he and Dr. Brodie will publish their own findings in full.