Water Oxidation by [(tpy)(H2O)2RuIIIORuIII(H2O)2(tpy)]4+
- 19 November 1998
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 37 (25) , 6476-6484
- https://doi.org/10.1021/ic970908z
Abstract
The complex [(tpy)(C2O4)RuIIIORuIII(C2O4)(tpy)]·8H2O (1·8H2O) (tpy is 2,2‘:6‘,2‘‘-terpyridine) has been prepared and characterized by X-ray crystallography and FTIR, resonance Raman, and 1H NMR spectroscopies. From the results of the X-ray analysis, ∠RuORu is 148.5° with a torsional angle (O22−Ru2−O1−Ru1−O12) of 22.7° and there is a short Ru−O bridge distance of 1.843 Å. 1 undergoes a chemically reversible one-electron, pH-independent oxidation at 0.73 V vs NHE (0.49 V vs SCE) from pH = 4−8 and a pH-dependent, two-electron, chemically irreversible reduction at −0.35 V below pH = 4.0. Addition of 1·8H2O to strong acid generates [(tpy)(H2O)2RuIIIORuIII(H2O)2(tpy)]4+ (2), which has been characterized by UV−visible, resonance Raman, and 1H NMR measurements. In pH-dependent cyclic voltammograms there is evidence for a series of redox couples interrelating oxidation states from RuIIORuII to RuVORuV. In contrast to the “blue dimer”, cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+, oxidation state RuIVORuIV (RuVORuIII?) does appear as a stable oxidation state. Oxidation of RuIVORuIV by CeIV in 0.1 M HClO4 is followed by rapid O2 production and appearance of an anated form of RuIVORuIV. O2 formation is in competition with oxidative cleavage of RuVORuV by CeIV to give [RuVI(tpy)(O)2(OH2)]2+. Anation and oxidative cleavage prevent this complex from being a true catalyst for water oxidation.Keywords
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