Electron-transfer Kinetics of Transition-metal Complexes in Lower Oxidation States. Part I. Electron Spin Resonance Measurements of the Electron-exchange Rate between Cr(bipy)31+ and Cr(bipy)3

Abstract

The rate of the electron-exchange reaction between Cr(bipy)31+ and Cr(bipy)3 was measured in N,N-dimethylformamide by the ESR method, with the line-broadening procedure. The width of the partly-overlapped hyperfine lines was determined by comparing the observed spectrum with the computer-simulated one. The observed second-order rate constant was (1.5±0.4)×109 M−1 sec−1 at 25°C. When corrected for diffusion, this yielded the activation-controlled rate constant of 2.0×109 M−1 sec−1. It was pointed out that the rate constant obtained here was the largest of all those ever reported for the electron-exchange reactions in which the transition-metal complexes participated. The observed rate constant was in good agreement with the one calculated non-empirically according to the theory of R. A. Marcus. Although the value for the molecular radius must be chosen somewhat arbitrarily in applying this theory, the “good” radius was a reasonable one in view of the molecular geometry and dimensions of the reactants. The rate constant of the Heisenberg spin-exchange process was also determined to be 1.8×109 M−1 sec−1 at 25°C in the same solvent.

Photoinduced Electron Transfer Processes of CdPS3 Intercalated with Ruthenium Tris(bipyridyl) and Methylviologen Cations

“…We were able to generate a reasonable simulation 30 of this spectrum by assuming g ) 2.002 and six equivalent nitrogen nuclei having a nuclear hyperfine coupling constant of a N ) 7.05 G (Figure 5b). The spectrum is qualitatively similar to that obtained by Saji and Aoyagui 31 for the chromium tris(bipyridyl) compound, Cr(bipy) 3 + in solution at room temperature. The comparison suggests that the 13-line hyperfine spectrum, in both instances, arises from coupling to six equivalent nitrogen nuclei of the three equivalent bipyridyl ligands.…”

Low Work Function Reduced Metal Complexes as Cathodes in Organic Electroluminescent Devices

“…Although the solidstate conductivity of this system has not been reported, analysis of the electron-transfer reaction between [Cr(bpy) 3 ] 1+ and [Cr-(bpy) 3 ] 0 in N,N-dimethylformamide solution revealed a very fast second-order rate constant of 2.0 × 10 9 M -1 s -1 . 24 This rate was rationalized in part by minimal inner-sphere reorganization upon electron exchange, which would be expected for all of these complexes, and would also be consistent with facile electron transfer in the solid state.…”