Electroactive ligands

As a result of their low redox potentials [173], bis(phthalocyaninato) lanthanide complexes are often inadvertently reduced or oxidized, and they are also very sensitive to acids and bases. In order to solve these problems, Veciana et al. achieved certain success on designing a series of novel compounds with characteristics that would give them improved redox stability. Electroactive ligands based on phthalo-cyaninato tetra dicarboximide [175] or perfluorinated phthalocyanine [176] were used to assemble the double-decker lanthanide complexes, with the effect of stabilizing the negative charge of the anionic state of the compounds, which resulted in a strong shift of 0.7 V of their first oxidation potentials. 

The size-exclusion and ion-exchange properties of zeoHtes have been exploited to cause electroactive species to align at a zeoHte—water interface (233—235). The zeoHte thus acts as a template for the self-organization of electron transfer (ET) chains that may find function as biomimetic photosynthetic systems, current rectifiers, and photodiodes. An example is the three subunit ET chain comprising Fe(CN)g anion (which is charge-excluded from the anionic zeoHte pore stmcture), Os(bipyridine)3 (which is an interfacial cation due to size exclusion of the bipyridine ligand), and an intrazeoHte cation (trimethylamino)methylferrocene (F J ). A cationic polymer bound to the (CN) anion holds the self-assembled stmcture at an... 

Electropolymerization is also an attractive method for the preparation of modified electrodes. In this case it is necessary that the forming film is conductive or permeable for supporting electrolyte and substrates. Film formation of nonelectroactive polymers can proceed until diffusion of electroactive species to the electrode surface becomes negligible. Thus, a variety of nonconducting thin films have been obtained by electrochemical oxidation of aromatic phenols and amines Some of these polymers have ligand properties and can be made electroactive by subsequent inincorporation of transition metal ions... 

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. 

The first attempt to construct a dendrimer with an electroactive Ru-polypyridi-ne core was based on the reaction of Ru(bpy)2Cl2 with a branched polyether-substituted phenanthroline ligand (11) [27]. In the potential window +2/-2V, this compound shows a one-electron oxidation process and three distinct one-electron reduction processes that, by comparison with the behavior of the... 

Furthermore, it has been demonstrated that the successful electrocatalytic reduction of C02 with [Ru(bpy)2(CO)2]2+ in aqueous MeCN is mainly due to the formation of a polymeric electroactive film, which occurs during the reduction of the complex.91 This film is composed of an open cluster polymer [Ru(bpy)(CO)2]ra (Scheme 6) based upon extended Ru°—Ru° bonds. Electropolymerization of [Ru(bpy)2(CO)2]2+ results from the overall addition of two electrons per mole of [Ru(bpy)2(CO)2]2+ and is associated with the decoordination of one bpy ligand (Equation (33)). 

Inner-sphere electrode processes are defined as those in which the electron exchange occurs between the electrode and the electroactive species (the metal core or its ligand) that are in direct contact with the electrode surface, see Figure 2. 

The usual situation we encounter is that where the ligands are electro-inactive but the cation is electroactive, both before and after complexation. However, the potential at which reduction occurs will shift following complexation reduction of the uncomplexed cation is characterized by a half-wave potential, i/2(tree),... 

Kinetic Scheme. Generally, metal ions in a solution for electroless metal deposition have to be complexed with a ligand. Complexing is necessary to prevent formation of metal hydroxide, such as Cu(OH)2, in electroless copper deposition. One of the fundamental problems in electrochemical deposition of metals from complexed ions is the presence of electroactive (charged) species. The electroactive species may be complexed or noncomplexed metal ion. In the first case, the kinetic scheme for the process of metal deposition is one of simple charge transfer. In the second case the kinetic scheme is that of charge transfer preceded by dissociation of the complex. The mechanism of the second case involves a sequence of at least two basic elementary steps ... 

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