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Isolated Seven-Coordinate Ru(IV) Dimer Complex with HOHOH (-) Bridging Ligand as an Intermediate for Catalytic Water Oxidation
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0003-1662-5817
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0002-4521-2870
2009 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 30, 10397-+ p.Article in journal (Refereed) Published
Abstract [en]

With the inspiration from an oxygen evolving complex (OEC) in Photosystern II (PSII), a mononuclear Ru(II) complex with a tetradentate ligand containing two carboxylate groups has been synthesized and structurally characterized. This Ru(II) complex showed efficient catalytic properties toward water oxidation by the chemical oxidant cerium(IV) ammonium nitrate. During the process of catalytic water oxidation, Ru(III) and Ru(IV) species have been successfully isolated as intermediates. To our surprise, X-ray crystallography together with HR-MS revealed that the Ru(IV) species is a seven-coordinate Ru(IV) dimer complex containing a [HOHOH](-) bridging ligand. This bridging ligand has a short O center dot center dot center dot O distance and is hydrogen bonded to two water molecules. The discovery of this very uncommon seven-coordinate Ru(IV) dimer together with a hydrogen bonding network may contribute to a deeper understanding of the mechanism for catalytic water oxidation. It will also provide new possibilities for the design of more efficient catalysts for water oxidation, which is the key step for solar energy conversion into hydrogen by tight-driven water splitting, the ultimate challenge in artificial photosynthesis.

Place, publisher, year, edition, pages
2009. Vol. 131, no 30, 10397-+ p.
URN: urn:nbn:se:kth:diva-18657DOI: 10.1021/ja9034686ISI: 000268644400031ScopusID: 2-s2.0-68049108505OAI: diva2:336704
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-09-22Bibliographically approved
In thesis
1. Artificial Water Splitting: Ruthenium Complexes for Water Oxidation
Open this publication in new window or tab >>Artificial Water Splitting: Ruthenium Complexes for Water Oxidation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the development and study of Ru-based water oxidation catalysts (WOCs) which are the essential components for solar energy conversion to fuels. The first chapter gives a general introduction about the field of homogenous water oxidation catalysis, including the catalytic mechanisms and the catalytic activities of some selected WOCs as well as the concerns of catalyst design. The second chapter describes a family of mononuclear Ru complexes [Ru(pdc)L3] (H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) towards water oxidation. The negatively charged pdc2 dramatically lowers the oxidation potentials of Ru complexes, accelerates the ligand exchange process and enhances the catalytic activity towards water oxidation. A Ru aqua species [Ru(pdc)L2(OH2)] was proposed as the real catalyst. The third chapter describes the analogues of [Ru(terpy)L3]2+ (terpy = 2,2′:6′,2′′-terpyridine). Through the structural tailor, the ligand effect on the electrochemical and catalytic properties of these Ru complexes was studied. Mechanistic studies suggested that these Ru-N6 complexes were pre-catalysts and the Ru-aqua species were the real WOCs. The forth chapter describes a family of fast WOCs [Ru(bda)L2] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Catalytic mechanisms were thoroughly investigated by electrochemical, kinetic and theoretical studies. The main contributions of this work to the field of water oxidation are (i) the recorded high reaction rate of 469 s−1; (ii) the involvement of seven-coordinate Ru species in the catalytic cycles; (iii) the O-O bond formation pathway via direct coupling of two Ru=O units and (iv) non-covalent effects boosting up the reaction rate. The fifth chapter is about visible light-driven water oxidation using a three component system including a WOC, a photosensitizer and a sacrificial electron acceptor. Light-driven water oxidation was successfully demonstrated using our Ru-based catalysts.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 80 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2011:48
water oxidation, ruthenium, electrochemistry, DFT calculation, photoelectrochemistry, negatively charged ligand, catalyst
National Category
Organic Chemistry
urn:nbn:se:kth:diva-40848 (URN)978-91-7501-083-0 (ISBN)
Public defence
2011-10-07, E3, Osquars backe 14, KTH, Stockholm, 10:00 (English)
QC 20110922Available from: 2011-09-22 Created: 2011-09-21 Last updated: 2011-09-22Bibliographically approved

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