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Apparent reduction of ruthenium trimers by hydroxide ion

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Apparent reduction of ruthenium trimers by hydroxide ion
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  J. Ulor e. nml. Chem. 1974. Vol. 36 p. 2385. Pergamon Press. Printed in Great Britain. NOT S pparent reduction of ruthenium trimers by hydroxide ion (Received 12 October 1973) EARHER communications[l, 2] reported a remarkable reac- tion in which NH3)sRuORu NH3)4ORu NH3); + here- after 1) reacted with hydroxide ion to produce the corres- ponding 6 + cation hereafter II). We now report additional data and a new interpretation of this unusual reaction. We have studied this reaction using a commercial oxygen- sensor a gold electrode covered by an oxygen-permeable membrane). No oxygen* was found to be evolved either in this reaction or in the reaction of [C1Rh py)4OORh py),~C1] 3 + with[3] OH-, although 02 was readily detectable in the reaction of Fe bipy)~ + with[4] OH- and CrO~- with[5] H +. When acidic solutions of I :~re electrolyzed at platinum electrodes or treated with chemical oxidizing and reducing agents, a variety of new species can be produced; many of these have only a single intense absorption peak in the u.v.-visible-N1R regions of the spectrum. In several but not all) cases, it is possible rapidly to reconvert these new species to I or II by gentle treatment. The intense absorption characteristic of these species indicates that they are Ru .dimers or other polymers, and those that readily yield I or 11 are taken to be trimers. It was previously reported that Ru HaO)~ + is a catalyst for the reaction of I with OH . Ru N H 3)sH 2 ° 3 + has some catalytic activity and compounds containing carboxyl groups inhibit the reaction, but none of the reduced or oxidized trimeric or polymeric) species just described has a significant effect on the reaction of 1 and OH- when it is added to the reaction mixture. Several of the new species just described are present as impurities irr most preparations of both I and 1I; oxidation of II to 1 is invariably accompanied by formation of greater or lesser concentrations of a substance which is more highly oxidized than I apparently a trimer of Ru 1V)). Reaction of aliquots of solutions of I with OH-, yields between 80 and 100 per cent as much lI as is produced by reduction of aliquots of the same solutions at platinum electrodes. Interpretation of these results is complicated by the possibility that, at the electrode, Ru 1V) trimers, present along with 1, may also be reduced to II. An interpretation of the overall stoichiometry of this reaction which is consistent with our present results, as well as with data reported earlier, is the following: 8 NHa)sRuORu NH3),~ORu NH3)~* + 4H20 + 6OH ; Ru 3 + 7 NH3}sRuORu NH3)4ORu NH~) ~ +3RuO.~ a 14NH2, On this basis, the slower reactions which follow[2] the rapid change of visible-region chromophore are considered to be interactions of intermediate species in which Ru has oxi- dation states of four or higher. Acknowledgement--We are grateful for support under National Science Foundation Grant GP-32188. JOSEPH E. EARLEY HOSSEIN RAZAVI PURUSHOTHAMAN CHALILPOYIL Department of Chemistry Georgetown University Washington, D.C. REFEREN ES I. J. E. Earley and T. Fealey, lnorg. Chem. 12, 323 11973). 2. J. E. Earley and H. Razavi, Inmi~. natl. ( hem. Lett. 9, 331 1973). 3. a) A. W. Addison amt R. D. Giltard, ,I. (hvm. Soc. A), 2523 1970). b) R. Eley and J. E. Earley: ]. York and J. E. Earley, Abstracts Middle Atlantic Regional Meeting. ACS, 1973. c) F. Czulada and J. E. Earley, 1 n preparahon disproportionation mechanisms seem to occur in this system also). 4. G. Nord and O. Wernberg, J. chem. Soc. (Dalton~ 866 1972). 5. D. Quane and J E. Earley. J, .4m. chem. Soc. 87. 3823 1965). *Using a Beckman oxygen electrode and associated electronics, the amount of oxygen produced was less than 5 per cent of that expected on the basis of the amount of oxidant consumed. 2385
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