Abstract
Low-temperature resonance Raman (RR) spectra of the dimeric Ru{sup III}Ru{sup IV} ion formed by oxidation of Ru(edta)OH{sub 2}{sup {minus}} exhibited a prominent band at 433 cm{sup {minus}1}, which shifted to 431 cm{sup {minus}1} upon substitution of ({sup 18}O)-H{sub 2}O in the primary coordination sphere of the precursor ion. A second band, at 324 cm{sup {minus}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 {mu}-oxo ion, i.e. (Ru(edta)){sub 2}O{sup 3{minus}}; from the magnitude of the isotopic shifts, the Ru-O-Ru angle was estimated to be 165{degree}. The reduction potential for the Ru{sup IV}{sub 2}/Ru{sup III}Ru{sup IV} couple was acid-insensitive over the range pH 2-11, suggesting that the dimer does not contain coordinated H{sub 2}O in either oxidation state. Cyclic voltammographic results in neutral solution suggested that (Ru(edta)){sub 2}O{sup 2{minus}} 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 O{sub 2} among the gaseous products. Instead, copious quantities of CO{sub 2} were formed, the source of which was coordinated EDTA. 29 refs., 8 figs., 1 tab.
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