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Synthesis and characterization of dinuclear ruthenium complexes covalently linked to Ru(II) tris-bipyridine: an approach to mimics of the donor side of photosystem II
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
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2005 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, no 24, 7305-7314 p.Article in journal (Refereed) Published
Abstract [en]

The structural rearrangements triggered by oxidation of the dinuclear Mn complex [Mn2(bpmp)(u-OAc)2]+ (bpmp = 2,6-bis[bis(2-pyridylmethyl)amino]methyl-4-methylphenol anion) in the presence of water have been studied by combinations of electrochemistry with IR spectroscopy and with electrospray ionization mass spectrometry (ESI-MS). The exchange of acetate bridges for water (D2O) derived ligands in different oxidation states could be monitored by mid-IR spectroscopy in CD3CN-D2O mixtures following the Vas(C-O) bands of bound acetate at 1594.4 cm-1 (II,II), 1592.0 cm-1 (II,III) and 1586.5 cm-1 (III,III). Substantial loss of bound acetate occurs at much lower water content (<0.5% v/v) in the III,III state than in the II,II and II,III states (>10%). The ligand-exchange reactions do not initially reduce the overall charge of the complex but facilitate further oxidation by proton-coupled electron transfer as the water-derived ligands are increasingly deprotonated in higher oxidation states. In the IR spectra deprotonation could be followed by the formation of acetic acid (DOAc, ~1725 cm-1, V(C-O)) from the released acetate (1573.6 cm-1, Vas(C-O)). By the on-line combination of an electrochemical flow cell with ESI-MS several product complexes could be identified. A di-u-oxo bridged III,IV dimer [Mn2(bpmp)(u-O)2]2+ (m/z 335.8) can be generated at potentials below the III,III/II,III couple of the di-u-acetato complex (0.61 V Vs. ferrocene). The ligand-exchange reactions allow for three metal-centered oxidation steps to occur from II,II to III,IV in a potential range of only 0.5 V, explaining the formation of a spin-coupled III,IV dimer by photo-oxidation with [Ru(bpy)3]3+ in previous EPR studies.

Place, publisher, year, edition, pages
2005. Vol. 11, no 24, 7305-7314 p.
Keyword [en]
electrochemistry, electron transfer, mixed-valent compounds, ruthenium cluster, sensitizers
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-95873DOI: 10.1002/chem.200500592PubMedID: 16163754OAI: oai:DiVA.org:uu-95873DiVA: diva2:170239
Available from: 2007-05-04 Created: 2007-05-04 Last updated: 2015-06-01
In thesis
1. Molecular Approaches to Photochemical Solar Energy Conversion: Towards Synthetic Catalysts for Water Oxidation and Proton Reduction
Open this publication in new window or tab >>Molecular Approaches to Photochemical Solar Energy Conversion: Towards Synthetic Catalysts for Water Oxidation and Proton Reduction
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A molecular system capable of photoinduced water splitting is an attractive approach to solar energy conversion. This thesis deals with the functional characterization of molecular building blocks for the three principal functions of such a molecular system: Photoinduced accumulative charge separation, catalytic water oxidation, and catalytic proton reduction.

Systems combining a ruthenium-trisbipyridine photosensitizer with multi-electron donors in form of dinuclear ruthenium or manganese complexes were investigated in view of the rate constants of electron transfer and excited state quenching. The kinetics were studied in the different oxidation states of the donor unit by combination of electrochemistry and time resolved spectroscopy. The rapid excited state quenching by the multi-electron donors points to the importance of redox intermediates for efficient accumulative photooxidation of the terminal donor.

The redox behavior of manganese complexes as mimics of the water oxidizing catalyst in the natural photosynthetic reaction center was studied by electrochemical and spectroscopic methods. For a dinuclear manganese complex ligand exchange reactions were studied in view of their importance for the accumulative oxidation of the complex and its reactivity towards water. With the binding of substrate water, multiple oxidation in a narrow potential range and concomitant deprotonation of the bound water it was demonstrated that the manganese complex is capable of mimicking multiple aspects of photosynthetic water oxidation.

A dinuclear iron complex was investigated as biomimetic proton reduction catalyst. The complex structurally mimics the active site of the iron-only hydrogenase enzyme and was designed to hold a proton on the bridging ligand and a hydride on the iron centers. Thermodynamics and kinetics of the protonation reactions and the electrochemical behavior of the different protonation states were studied in view of their potential catalytic performance.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 76 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 306
Physical chemistry, artificial photosynthesis, solar fuel, WOC, OEC, accumulative electron transfer, hydrogenase mimic, oxygen evolution, proton reduction, water oxidation, Fysikalisk kemi
urn:nbn:se:uu:diva-7875 (URN)978-91-554-6889-7 (ISBN)
Public defence
2007-05-28, Häggsalen, Ångström, Uppsala, 10:00
Available from: 2007-05-04 Created: 2007-05-04Bibliographically approved

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