Electronic Structure and Substitution and Redox Reactivity of Imidazolate-Bridged Complexes of Pentacyanoferrate and Pentaammineruthenium

Abstract

The mixed-valence compound [(NC)(5)Fe(II)-Im-Ru(III)(NH(3))(5)](-),M(i), was prepared in solution and as a solid sodium salt from [Fe(CN)(5)H(2)O](3)(-) and [Ru(NH(3))(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 979 nm (epsilon = 962 M(-)(1) cm(-)(1)) associated with an intervalence transition. By calculation of the Hush model parameters alpha(2) and H(ab) (delocalization and electronic coupling factors, respectively), the complex is defined as a valence-trapped Fe(II)-Ru(III) system; this is confirmed by the measured redox potentials at -0.20 V and 0.30 V, associated with redox processes at the ruthenium and iron center, respectively. The formation stability constant of the mixed-valence ion was obtained through independent measurements of k(f) and k(d), the formation and dissociation specific rate constants, respectively. The stabilization of M(i) with respect to disproportionation into the isovalent states, 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 oxidized (O(i)) binuclear complexes were prepared in solution and characterized by UV-vis spectroscopy. The kinetics of the reactions of R(i) and M(i) with peroxydisulfate were measured and a mechanistic analysis was performed, showing the relevance of electronic isomerization in completing 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 related complexes comprising different X(5)M-L moieties bound to Ru(II)(NH(3))(5)(2+). A linear correlation is displayed by plotting ln k(et) against E degrees (Ru), associated with the intramolecular oxidation rate constant of Ru(II) in the ion pair (binuclear species + peroxydisulfate) and the reduction potential of the corresponding Ru(III,II) couple in the ion pair.

Discrete Cyanide‐Bridged Mixed‐Valence Co/Fe Complexes: Outer‐Sphere Redox Behaviour

“…The thermal activation parameters are clearly dominated by the electrostriction occurring on outer-sphere precursor formation, while the trends found for the values of the volume of activation indicate an important degree of tuning due to the charge distribution during the electron transfer process. The special arrangement on the amine ligands in the isomer trans-[L 14 Co III NCFe II (CN) 5 ] − accounts for important differences in solvent-assisted hydrogen bonding occurring within the outer-sphere redox process, as has been established in redox reactions of similar compounds.…”

“…[7Ϫ9] During this period, a few redox studies on discrete dinuclear Fe/Ru mixedvalence compounds have appeared, [14,15] but neither the pH Scheme 1 dependence of such reactions nor the use of transition metal complexes as redox partners has been examined. Furthermore, the stability and full characterisation of the complexes involved was not achieved in some cases.…”

Ternary adduct {[W(CN)8]3−,[Pt(en)2]2+,[W(CN)8]3−} in aqueous solution and crystal structure of [Pt(en)2]3[W(CN)8]2·4H2O with infinite linear W · · · Pt chains

“…2 The crucial role of the more reactive electronic isomers [Ru II -L-Fe III ] present in binuclear [Ru II -L-Fe III ] bridged systems in their redox reactivity has been investigated thoroughly. 3 The first spectroscopic and X-ray evidence for the non-bridged heterobinuclear mixedvalence [Pt(NH 3 ) 4 ] 2 [W(CN) 8 ][NO 3 ]ؒ2H 2 O complex that exists as a borderline localised-to-delocalised system has been found in our previous studies. 4, 5 The substantial electronic delocalisation has been created by the stereochemical barrier to the innersphere two-electron oxidation of [Pt(NH 3 ) 4 ] 2ϩ by [W(CN) 8 ] 3Ϫ .…”

4,4‘-Dipyridylamine-Bridged Binuclear Complexes of Pentacyanoferrate and Pentaammineruthenium

“…In recent years there have been numerous studies on the binuclear complexes of pentacyanoferrate(II,III) and pentaammineruthenium(II,III). − In addition to the investigations in the spectral and electrochemical aspects which are usually emphasized in the mixed-valence chemistry of the diruthenium system, the research works of this system have been extended to the study of the reactivity of the mixed valence compounds. ,, Nevertheless, most of the previous works in the characterization of the binuclear complexes of this kind were focused on both the reduced form and the mixed valence species; and little effort has been devoted to the investigation of the oxidized form. One of the reasons may be the difficulty in the detection of the species due to the lack of the spectral characteristics.…”