Experimental demonstration of radicaloid character in a RuV=O intermediate in catalytic water oxidation |
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| Authors: | Dooshaye Moonshiram Igor Alperovich Javier J. Concepcion Thomas J. Meyer Yulia Pushkar |
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| Affiliation: | aDepartment of Physics, Purdue University, West Lafayette, IN, 47907;;bResearch Center for Nanoscale Structure of Matter, Southern Federal University, Rostov-on-Don 344090, Russia; and;cDepartment of Chemistry, University of North Carolina, Chapel Hill, NC, 27599 |
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| Abstract: | Water oxidation is the key half reaction in artificial photosynthesis. An absence of detailed mechanistic insight impedes design of new catalysts that are more reactive and more robust. A proposed paradigm leading to enhanced reactivity is the existence of oxyl radical intermediates capable of rapid water activation, but there is a dearth of experimental validation. Here, we show the radicaloid nature of an intermediate reactive toward formation of the O-O bond by assessing the spin density on the oxyl group by Electron Paramagnetic Resonance (EPR). In the study, an 17O-labeled form of a highly oxidized, short-lived intermediate in the catalytic cycle of the water oxidation catalyst cis,cis-[(2,2-bipyridine)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ was investigated. It contains Ru centers in oxidation states [4,5], has at least one RuV = O unit, and shows |Axx| = 60G 17O hyperfine splittings (hfs) consistent with the high spin density of a radicaloid. Destabilization of π-bonding in the d3 RuV = O fragment is responsible for the high spin density on the oxygen and its high reactivity. |
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| Keywords: | blue dimer water splitting catalysis solar fuels |
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