Complexes redox behaviour

Within the large number of multiredox arrays containing metalloporphyrins/covalently bound (conjugate) fullerene-metalloporphyrin dyads have gained enormous interest in the last ten years, mainly due to their potential application as artificial antennae Due to the multiredox behaviour of the fullerenes (up to six reversible one-electron reductions and at least one reversible one-electron oxidation), the porphyrin ligands and the incorporated metals, the assignment of electron-transfer steps in such systems is difficult. Recently, spectroelectrochemical characterisation has been carried out on a number of fullerene-[(TPP)Co] dyads shown in Scheme 4.3, which exhibit rather complex redox behaviour (Figure 4.19). 

The redox behaviour of transition metal complexes with soft ligands. E. Uhlig, Comments Inorg. Chem., 1981,1,169-182 (43). 

Barranco, E.M., Crespo, O., Gimeno, M.C., Jones, P.G., Laguna, A. and Villacampa, M.D. (1999) Synthesis, structure and redox behaviour of gold and silver complexes with 3-ferrocenylpyridine. Journal of Organometallic Chemistry, 592, 258. 

It needs to be pointed out that E values may also be quite sensitive to the nature of the solvent and supporting electrolyte used for an electrochemical study. Apart from solvation effects of the non-specific type, solvent molecules may occupy coordination sites in either the starting complex or the products and hence influence redox behaviour (Fabbrizzi, 1985). Similarly, the nature of the anion present may also strongly influence the redox potential if it has ligating properties (Zeigerson etal., 1982). Because of such effects, caution needs to be exercised in attempting to compare electrochemical data which have not been obtained under similar conditions. 

The ability of thioether macrocyclic complexes (and especially those of [9]aneS3) to support multi-redox behaviour at the coordinated metal centre is particularly notable. This allows a series of reversible stepwise one-electron oxidation and/or reduction processes, and stabilization of highly unusual transition metal oxidation states e.g. mononuclear [Pd([9]aneS3)2]2+/3+/4+,149 [Au([9]aneS3)2]+/2+/3+,150 [Ni([9]aneS3)2]2+/3+,151 and [Rh([9]aneS3)2]+/2+/3+.152 It appears to be the ability of the crown thioethers to readily adjust their... 

The redox behaviour of this vanadium(IV) complex is shown in Figure 5.11... 

The redox behaviour of cobalt complexes is fairly similar to that of iron... 

In coordinating solvents, such as MeCN and dmso, [Cu(dpa)2]2+ binds two solvent molecules becoming hexacoordinate. In contrast in non-coordinating solvents the complex maintains its tetracoordination. Figure 118 just shows the redox behaviour of the complex in noncoordinating nitromethane solution.175... 

To understand these complex catalysts we describe some basic HTSC (high Tc) oxides and the important role played by EM in elucidating the nanostructure and chemistry of these complex oxides. The redox behaviour of Cu in various oxidation states of HTSC may be important in environmental control catalysis. 

Review work for future updates of our data base should focus on iron compounds and complexes. The iron system is thought to be of crucial importance for characterizing the redox behaviour of radioactive waste repositories. Preliminary applications have indicated that the lack of data for the iron system is a source of major uncertainties associated with the definition of an oxidation potential. Hence, there is little use in developing sophisticated redox models for radionuclides as long as the dominant redox processes in a repository are poorly known. 

The dismutation reaction of a mixture of flavoquinone and flavohydroquinone in DMF was studied kinetically in the presence and absence of redox-inactive metal ions This system shows a very complex kinetic behaviour with the formation... 

One oxochromium(V) complex, CrO(TETMC), containing the trinegative anion of a corrole (279), has been characterized as the solid.1266 It is prepared (Table 102) simply by exposure to air of a solution presumably containing a Cr11 complex. Aerial oxidation of Cr (TPP) produces the oxochromium(IV) complex CrO(TPP) so the corrole ligand apparently facilitates autoxida-tion. The redox behaviour of CrO(TETMC) has been examined by cyclic voltametry.1267... 

Interesting redox behaviour is exhibited by the complexes [MoOL] where L is a tetradentate S,S, IV,IV aromatic aminothiol group (N, N -bis-2 -mercaptophenyl-1,2-... 

Although the detailed mechanism of electron transport and transfer involving PVF electrodes may be complex, they show remarkable stability and rapidly reversible redox behaviour in non-aqueous solvents such as acetonitrile. This has led to the suggestion69 that they might function as standard electrodes for non-aqueous solvents. Such standards are required since the SCE is unsatisfactory in a number of respects. Particularly, the liquid junction potential between aqueous and non-aqueous solutions is unknown and irreprodudble also there is a danger that the test solution will become contaminated with water and with potassium and sodium ions. 

Voltammetric sensors Here, detection is based on the redox behaviour of the analyte on the electrode. However, when the analyte is bound to suspended particles or present in complexes that are chemically inert, direct determination is generally not possible. Therefore, voltammetric sensors provide information on the species that are chemically available (labile). Uniquely, these sensors typically involve a necessary preconcentration step in which the analyte is usually reduced and accumulated for a certain time at the electrode. This process is followed by its oxidation and stripping from the electrode. Whole family of methods has emerged based on the different potential-current profiles for the stripping step, all having common name Stripping Analysis (SA). 

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