Electronic Structure of the Water Oxidation Catalyst cis , cis -[(bpy) ₂ (H ₂ O)Ru ^III ORu ^III (OH ₂ )(bpy) ₂ ] ⁴⁺ , The Blue Dimer

Journal Article · Wed Jan 18 00:00:00 EST 2012 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic201521w· OSTI ID:1387114

Jurss, Jonah W. ^[1]; Concepcion, Javier J. ^[1]; Butler, Jennifer M.; Omberg, Kristin M.; Baraldo, Luis M.; Thompson, Darla Graff; Lebeau, Estelle L.; Hornstein, Brooks; Schoonover, Jon R.; Jude, Hershel; Thompson, Joe D.; Dattelbaum, Dana M.; Rocha, Reginaldo C.; Templeton, Joseph L. ^[1]; Meyer, Thomas J. ^[1]

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1. Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States

The first designed molecular catalyst for water oxidation is the “blue dimer”, cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(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 RuIII 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 pKa 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 RuIII 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 (dπ1*)2 with a low-lying, paramagnetic triplet state (dπ1*)1(dπ2*)1. Systematic structural–magnetic–IR correlations are observed between νsym(RuORu) and νasym(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 $$\angle$$ Ru–O–Ru dictated by the distortion and electron–electron repulsion.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: SC0001011
• OSTI ID: 1387114
• Journal Information: Inorganic Chemistry, Vol. 51, Issue 3; Related Information: UNC partners with University of North Carolina (lead); Duke University; University of Florida; Georgia Institute of Technology; University; North Carolina Central University; Research Triangle Institute; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
catalysis (homogeneous)
catalysis (heterogeneous)
solar (photovoltaic)
solar (fuels)
photosynthesis (natural and artificial)
hydrogen and fuel cells
electrodes - solar
charge transport
materials and chemistry by design
synthesis (novel materials)
synthesis (self-assembly)