STRUCTURE AND WATER-OXIDIZING CAPABILITIES OF DIMERIC RUTHENIUM EDTA COMPLEX-IONS

Low-temperature resonance Raman (RR) spectra of the dimeric RuIIIRuIVion formed by oxidation of Ru(edta)OH2-exhibited a prominent band at 433 cm−1, which shifted to 431 cm−1upon substitution of [180]-H20 in the primary coordination sphere of the precursor ion. A second band, at 324 cm−1, underwent a comparable isotope-dependent shift to lower energies. The RR spectra were insensitive to deuterium substitution. These features establish that the dimer is a μ-oxo ion, i.e., [Ru(edta)]203-; from the magnitude of the isotopic shifts, the Ru-O-Ru angle was estimated to be 165°. The reduction potential for the RuIV2/RuIIIRulvcouple was acid-insensitive over the range pH 2−11, suggesting that the dimer does not contain coordinated H20 in either oxidation state. Cyclic voltammographic results in neutral solution suggested that [Ru(edta)]202-was unstable with respect to decomposition. A reinvestigation of the water-oxidizing capabilities of this ion by polarographic, gas chromatographic, and mass spectrometric methods failed to reveal 02among the gaseous products. Instead, copious quantities of CO2were formed, the source of which was coordinated EDTA. © 1990, American Chemical Society. All rights reserved.