Estelle L Lebeau

Publications (2)4.6 Total impact

• Article: Electronic structure of the water oxidation catalyst cis,cis-[(bpy)2(H2O)Ru(III)ORu(III)(OH2)(bpy)2]4+, the blue dimer.

  Jonah W Jurss, Javier J Concepcion, Jennifer M Butler, Kristin M Omberg, Luis M Baraldo, Darla Graff Thompson, Estelle L Lebeau, Brooks Hornstein, Jon R Schoonover, Hershel Jude, Joe D Thompson, Dana M Dattelbaum, Reginaldo C Rocha, Joseph L Templeton, Thomas J Meyer
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  ABSTRACT: The first designed molecular catalyst for water oxidation is the "blue dimer", cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+). Although there is experimental evidence for extensive electronic coupling across the μ-oxo bridge, results of earlier DFT and CASSCF calculations provide a model with magnetic interactions of weak to moderately coupled Ru(III) ions across the μ-oxo bridge. We present the results of a comprehensive experimental investigation, combined with DFT calculations. The experiments demonstrate both that there is strong electronic coupling in the blue dimer and that its effects are profound. Experimental evidence has been obtained from molecular structures and key bond distances by XRD, electrochemically measured comproportionation constants for mixed-valence equilibria, temperature-dependent magnetism, chemical properties (solvent exchange, redox potentials, and pK(a) values), XPS binding energies, analysis of excitation-dependent resonance Raman profiles, and DFT analysis of electronic absorption spectra. The spectrum can be assigned based on a singlet ground state with specific hydrogen-bonding interactions with solvent molecules included. The results are in good agreement with available experimental data. The DFT analysis provides assignments for characteristic absorption bands in the near-IR and visible regions. Bridge-based dπ → dπ* and interconfiguration transitions at Ru(III) appear in the near-IR and MLCT and LMCT transitions in the visible. Reasonable values are also provided by DFT analysis for experimentally observed bond distances and redox potentials. The observed temperature-dependent magnetism of the blue dimer is consistent with a delocalized, diamagnetic singlet state (dπ(1)*)(2) with a low-lying, paramagnetic triplet state (dπ(1)*)(1)(dπ(2)*)(1). Systematic structural-magnetic-IR correlations are observed between ν(sym)(RuORu) and ν(asym)(RuORu) vibrational energies and magnetic properties in a series of ruthenium-based, μ-oxo-bridged complexes. Consistent with the DFT electronic structure model, bending along the Ru-O-Ru axis arises from a Jahn-Teller distortion with ∠Ru-O-Ru dictated by the distortion and electron-electron repulsion.
  Inorganic Chemistry 02/2012; 51(3):1345-58. · 4.60 Impact Factor
• Article: Water Oxidation by [(tpy)(H2O)2RuIIIORuIII(H2O)2(tpy)]4+

  Estelle L. Lebeau, S. Ajao Adeyemi, Thomas J. Meyer
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  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.
  11/1998;