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Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O
Department of Physics, Purdue University, 525 Northwestern West Lafayette, IN 47907, USA
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
* Author to whom correspondence should be addressed.
Received: 19 November 2012; in revised form: 5 January 2013 / Accepted: 23 January 2013 / Published: 30 January 2013
Abstract: Water oxidation is critically important for the development of energy solutions based on the concept of artificial photosynthesis. In order to gain deeper insight into the mechanism of water oxidation, the catalytic cycle for the first designed water oxidation catalyst, cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (bpy is 2,2-bipyridine) known as the blue dimer (BD), is monitored in D2O by combined application of stopped flow UV-Vis, electron paramagnetic resonance (EPR) and resonance Raman spectroscopy on freeze quenched samples. The results of these studies show that the rate of formation of BD[4,5] by Ce(IV) oxidation of BD[3,4] (numbers in square bracket denote oxidation states of the ruthenium (Ru) centers) in 0.1 M HNO3, as well as further oxidation of BD[4,5] are slower in D2O by 2.1–2.5. Ce(IV) oxidation of BD[4,5] and reaction with H2O result in formation of an intermediate, BD[3,4]′, which builds up in reaction mixtures on the minute time scale. Combined results under the conditions of these experiments at pH 1 indicate that oxidation of BD[3,4]′ is a rate limiting step in water oxidation with the BD catalyst.
Keywords: Ru complexes; catalysis of water oxidation; deuterium isotope effect; time-resolved X-band EPR spectroscopy; time-resolved resonance Raman; UV-Vis stopped flow kinetics
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Moonshiram, D.; Purohit, V.; Concepcion, J.J.; Meyer, T.J.; Pushkar, Y. Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O. Materials 2013, 6, 392-409.
Moonshiram D, Purohit V, Concepcion JJ, Meyer TJ, Pushkar Y. Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O. Materials. 2013; 6(2):392-409.
Moonshiram, Dooshaye; Purohit, Vatsal; Concepcion, Javier J.; Meyer, Thomas J.; Pushkar, Yulia. 2013. "Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O." Materials 6, no. 2: 392-409.