Structural investigations of the catalytic mechanisms of water oxidation by the [(bpy){sub 2}Ru(OH{sub 2})]{sub 2}O{sup 4+} ion
- Oregon Graduate Institute, Portland, OR (United States)
Electron paramagnetic resonance and Raman spectroscopies have been used to identify component species in acidic solutions containing the water oxidation catalyst ({mu}-oxo)bis[cis-aquabis(2,2{prime}-bipyridine)ruthenium(III)] ([3,3]) and Ce{sup 4+} ions. One-electron oxidation with Ce{sup 4+} gave rise to an anisotropic pH-dependent EPR signal at g = 1.77 {minus} 1.90, assigned to the S = 1/2 ground state of a spin-delocalized Ru-O-Ru orbital. Appearance of the EPR signal correlated with formation of a resonance-enhanced symmetric band at 4-05-410 cm{sup {minus}1} in the Raman spectrum, attributable to the Ru-O-Ru symmetric (v{sub s}) stretching mode. Upon further addition of Ce{sup 4+} in 0.1 M acid, a second anisotropic EPR signal was detected at g = 1.87, which correlated with a v{sub s}(Ru-O-Ru) band appearing at 398 cm{sup {minus}1}. By analogy with the one-electron oxidation product ([3,4]), this species was assigned as the S = 1/2 three-electron oxidized ion ([4,5]). In 1 M acid, however, the EPR spectrum of highly oxidized samples also exhibited an unusual isotropic signal centered as g = 1.95, whose relative intensity correlated with resonance Raman bands at {approximately}357 cm{sup {minus}1} (v{sub s}(Ru-O-Ru)) and 817 cm{sup {minus}1} (v(Ru=O)). By analogy with very similar signals reported for reduced Ru(bpy){sub 3}{sup +} ions and related species which contain bipyridine radical anions as ligands, the g = 1.95 signal is tentatively assigned to a coordinated bipyridine radical {pi}-cation in a complex whose metal oxidation state is [5,5].
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG06-87ER13664
- OSTI ID:
- 420945
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 20 Vol. 33; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
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