INTRAMOLECULAR ELECTRON TRANSFER THROUGH ISOMERIC FORMS OF DICYANOBENZENE

Article abstract of DOI:10.1021/j100407a038

Pentaamminecobalt(III)-μ-bis(nitrile)pentaamminerthenium(III) salts based on the three isomers of dicyanobenzene as the bridging groups have been prepared, and the rates of intramolecular electron transfer in the corresponding Co(III)-Ru(II) species have been measured as a function of temperature.The specific rates, s^-1 at 25 deg C, and the entropies of activation (cal mol^-1 K^-1) made from the three isomers of the bridging groups are para 4.2 x 10^-3, -3.5 +/- 1.0; meta 1.8 x10^-4, -10.5 +/- 2.0; ortho 1.9 x 10^-2, -0.5 +/- 2.0.The enthalpies of activation are, within experimental error, the same for the three systems.The lower rate for the 1,3 isomer as compared to the 1,4 isomer can reasonably be ascribed to the reaction being less adiabatic for the former bridging group.The increase rate for the 1,2 isomer is more difficult to understand, and it is only partly accounted for by considering the effect of metal-to-metal separation.