Ferrocene-ruthenium complexes

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

The tetranuclear complex [(Ru(NH3)5)4TCNE]8+ shows four, one electron oxidations and a one electron reduction.527 The 10+ is more stable than the 9+ and 11 + species, with a strong coupling between metal centres being proposed.527 A heteronuclear ferrocene-ruthenium complex [(Ru(NH3)5)2Fc(CN)2]4+ (Fc(CN)2 = l,l -dicyanoferrocene) has been prepared. No evidence was observed for an end to end interaction in the corresponding 5 + ion.547... 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

In contrast to ferrocenes, osmium and ruthenium complexes are capable of forming coordinative bonds with donor centers of GO including histidine imidazoles. There are therefore two ways of bringing coordinated transition metals onto enzyme surfaces, i.e., via natural and artificial donor sites. Artificial centers are commonly made of functionalized pyridines or imidazoles, which must be covalently attached to GO followed by the complexation of an osmium or... 

Whereas neither ferrocene nor OH-Tam had any effect on the ER-negative cells at 1 pM, the combination of the two motifs yielded highly toxic molecules. With the notable exception of a few ruthenium complexes [73,74], the anti-cancer properties... 

Figure 1. Comparison of iron and ruthenium oxidation in l,l -bis(diphenylphosphino)ferrocene-ruthenium(II) complexes (ESR spectra [44a] from electrolytically oxidized solutions of precursors [44b, c] in THE at 4 K) Oxidation of [Cp RuH(dppf), dppf= l,l -bis(diphenylphosphino)ferro-cene, and [(Cym)RuCl[dppf)](PF6), Cym = p-cymene, occurs at ruthenium for the former compound but yields a ferrocenium species for the latter.

Some accounts on the redox-induced switching of hyperpolarisabilities utilised penta-ammine ruthenium complexes bearing substituted 4,4 -bipyri-dinium coligands. The intense bipyridinium Ru LMCT band at 580 to 636 nm bleaches upon reduction of the metal centre, thus switching off their quadratic NLO response. The oxidation of the ferrocene donor in an ethenyl-linked ferrocene-nitrothiophene dyad likewise results in a decrease of the quadratic NLO response by about one order in magnitude. Oxidation-state-dependent quadratic NLO performance has also been noted by Lapinte and coworkers who compared the complexes Cp (dppe)Fe—C=CPh, Cp (dppe)Fe-C=C- 2(p-C6H4-l,4), Cp (dppe)Fe-C=C- 2(g-C6H4-l,3),... 

Some spectroscopic studies on metallocenes are as follows Gas phase syndiesis of unsymmetrically substituted ruthenocenes have been prqiared by gas phase electrocyclic reactions of pentadieny] ruthenium complexes. In the continuing soies of ptqiers on the Mdssbauer spectra of ferrocenes, azaferrocenes and phosphaferrocenes have been examined. H NMR studies have been carried out on the compounds of iod(4)iruthenoceniums(II,IV). A series of multinuclear NMR and X-ray single crystal diffraction shidies of metallocene containing cryptands has been carried out in addition to coordination studies of these species. ... 

More recently, a soluble polymer (32) was prepared via reaction of l,l -ferrocenedimethanol with 4,4 -biphenyltetraamine in the presence of [RuCl2(P(C6115)3)3] (70). Approximately 20% of the iron centers were foimd to be in the Fe(III) state as a result of oxidation by ruthenium complexes formed during the polycondensation reaction. Wright and co-workers have reported the synthesis of ferrocene-based polymers possessing nonlinear optical properties (33) (71-73). These polymers were formed by polycondensation of a difunctionabzed ferrocene monomer (71). 

On the other hand, the ruthenium complex of ferrocenyl-alkynyl dimer shows a separation of redox potentials of two ferrocene units through the alkyne-Ru-alkyne ligand at 0.22 This result indicates that the mixed-valence state of ferrocenyl groups in Ru(-C=C Fc)2(dppm)2 complex are much more stable because of the strong donor-acceptor interaction through the ruthenimn core metal with two a-bonding alkynyl chains. The four oxidation states could be experimentally foimd for Ru(H =C Fc)2(dppm)2 complex (Fe(II)-Ru(II) Fe(II) Fe(III) Ru(II) Fe(II) Fe(III) Ru(II)-Fe(in) Fe(III)-Ru(III)-Fe(III)), where the redox potential of the ruthenium center is positively shifted as noted above. 

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