ELECTRONIC-STRUCTURE AND SUBSTITUTION AND REDOX REACTIVITY OF IMIDAZOLATE-BRIDGED COMPLEXES OF PENTACYANOFERRATE AND PENTAAMMINERUTHENIUM

The mixed-valence compound [(NC)(5)Fe-II-Im-Ru-III(NH3)(5)](-),M(i), w as prepared in solution and as a solid sodium salt from [Fe(CN)(5)H2O] (3-) and [Ru(NH3)(5)Im](2+). The binuclear complex shows two bands at 366 nm (epsilon = 3350 M(-1) cm(-1)) and 576 nm (epsilon = 1025 M(-1) cm(-1)), assigned as LMCT transitions, as well as a near-IR band at 97 9 nm (epsilon = 962 M(-1) cm(-1)) associated with an intervalence tran sition. By calculation of the Hush model parameters alpha(2) and H-ab (delocalization and electronic coupling factors, respectively), the co mplex is defined as a valence-trapped Fe-II-Ru-III system; this is con firmed by the measured redox potentials at -0.20 V and 0.30 V, associa ted with redox processes at the ruthenium and iron center, respectivel y. The formation stability constant of the mixed-valence ion was obtai ned through independent measurements of k(f) and k(d), the formation a nd dissociation specific rate constants, respectively. The stabilizati on of M(i) with respect to disproportionation into the isovalent state s, as well as toward the formation of the electronic isomer, Fe-III-Im -Ru-II, was also estimated. The fully reduced (R(i)) and fully oxidize d (O-i) binuclear complexes were prepared in solution and characterize d by UV-vis spectroscopy. The kinetics of the reactions of R(i) and M( i) with peroxydisulfate were measured and a mechanistic analysis was p erformed, showing the relevance of electronic isomerization in complet ing the full conversion to O-i, through the assistance of the Ru-II(NH 3)(5)(2+) center in the oxidation of the neighboring Fe-II(CN)(5)(3-) moiety. The latter results are compared with those obtained with relat ed complexes comprising different X(5)M-L moieties bound to Ru-II(NH3) (5)(2+). A linear correlation is displayed by plotting ln k(et) agains t E degrees(Ru), associated with the intramolecular oxidation rate con stant of Ru-II in the ion pair (binuclear species + peroxydisulfate) a nd the reduction potential of the corresponding Ru-III,Ru-II couple in the ion pair.