Spectroelectrochemistry systems

The electrosynthesized (0EP)Ge(CgHs)C10, was characterized in situ by thin-layer spectroelectrochemistry. The final product of electrosynthesis was spectrally compared with the same compounds which were synthesized using chemical and photochemical methods(35). (0EP)Ge(C6H5)Ci and (0EP)Ge(CsHs)0H were also electrochemically generated by the use of specific solvent/supporting electrolyte systems(35). 

The anions [Ru2Xg] where X = C1, Br, and =1, 2, 3, or 4, have been investigated by spectroelectrochemistry. The Ru Ru complexes exhibit delocalization of electronic charge, the Ru Ru species has a strong Ru—Ru bonding interaction, and the more oxidized systems exhibit no metal-metal bonding interaction. " ... 

Electrochemically generated solutions of radical-cations will react with nucleophiles in an inert solvent to generate a radical intemiediate. Under these conditions the intermediate is oxidised to the carboniiim ion by a further radical-cation. Generally, an aromatic system is then reformed by loss of a proton. Reactions of 9,10-diphenylanthracene radical-cation nucleophiles in acetonitrile are conveniently followed either by stop flow techniques or by spectroelectrochemistry. Reaction with chloride ion follows the course shown in Scheme 6.2, where the termination... 

Spectroelectrochemistry with a thin-layer cell is used to determine the formal potential of a redox system. The absorption curves in Fig. 9.3 were obtained with a thin-layer cell containing a solution of jTclll(dmpe)2Br2]+ (dmpe = l,2-bis(dimethylphosphine)ethane) in 0.5 M Et4NCl04-DMF [4]. On each curve is... 

To a large extent, the discovery and application of adsorption phenomena for the modification of electrode surfaces has been an empirical process with few highly systematic or fundamental studies being employed until recent years. For example, successful efforts to quantitate the adsorption phenomena at electrodes have recently been published [1-3]. These efforts utilized both double potential step chronocoulometry and thin-layer spectroelectrochemistry to characterize the deposition of the product of an electrochemical reaction. For redox systems in which there is product deposition, the mathematical treatment described permits the calculation of various thermodynamic and transport properties. Of more recent origin is the approach whereby modifiers are selected on the basis of known and desired properties and deliberately immobilized on an electrode surface to convert the properties of the surface from those of the electrode material to those of the immobilized substance. 

Figure 6.22 Cell system for spectroelectrochemistry by use of optically transparent electrodes (OTEs).

The chemical stability and electrochemical reversibility of PVF films makes them potentially useful in a variety of applications. These include electrocatalysis of organic reductions [20] and oxidations [21], sensors [22], secondary batteries [23], electrochemical diodes [24] and non-aqueous reference electrodes [25]. These same characteristics also make PVF attractive as a model system for mechanistic studies. Classical electrochemical methods, such as voltammetry [26-28] chronoamperometry [26], chronopotentiometry [27], and electrochemical impedance [29], and in situ methods, such as spectroelectrochemistry [30], the SECM [26] and the EQCM [31-38] have been employed to this end. Of particular relevance here are the insights they have provided on anion exchange [31, 32], permselectivity [32, 33] and the kinetics of ion and solvent transfer [34-... 

The redox noninnocence of the 2-mercapto-3,5-di-tert-butylaniline ligand has recently been investigated with nF ions. The spectroelectrochemistry of the complex displays a range of electron transfers where the monocation, the neutral species, and the mono- and dianions have been characterized. In a related manner, Wieghardt and coworkers have reported the first example of a stable N, O-coordinated o-iminobenzoquinone via air oxidation of the initial nF complex with 2-anilino-4,6-di-tert-butylphenol (94). The analogous o-iminobenzosemiquinonate 7r-radical complex was also isolated for this system and earlier for the bis-(o-immobenzosemiquinonate)nickel(II) complex. ... 

Figure 44. Electrode systems for spectroelectrochemistry (a) optically transparent electrode, (b) electrode for internal reflection spectroscopy, and (c) electrode for specular reflectance spectroscopy.

Finally, the cation of a fascinating /i-C=C—C=C-bridged diruthenium complex shows IVCT bands characteristic of a class-III Robin-Day system.45 The FTIR spectroelectrochemistry also showed a 100 cm-1 shift in u(C=C) to lower frequencies, characteristic of cumulene-type chains. Data were also gathered for the complex after further oxidation. 

The IR spectroelectrochemistry of the mixed-valent heteropolyanions [PMo O ]"- (where n= 4, 5, 6, 7) suggests that these anions belong to the class II system in Robin and Day s classification of mixed-valence compounds. The spectra also showed evidence for decreased Mo=0 bond strength after reduction.171... 

Spectroelectrochemistry utilises the difference in the spectroscopic signature between the oxidised and the reduced form of a system to probe its redox properties. An incremental application of potential gradually changes the spectral profile of a system corresponding to the changes in the population of oxidised and reduced species. These spectral changes as a function of applied potential allow for the determination of various redox properties including, the... 

A very limited selection of examples will serve here to illustrate the power of the spectroelectrochemical approach, including optical spectro electrochemistry (Section 3.3), the selective but often most informative EPR spectroelectro-chemistry (Section 3.4 and Chapter 7), and the well-established but also increasingly employed infrared vibrational spectroelectrochemistry (Section 3.5 and Chapter 1). Although mainly transition-metal coordination compounds will be discussed, the previously mentioned extension of the concept and methodology to nonmetallic systems should be kept in mind. 

For the first reduction the IR shifts point to a porphyrin-centred electron transfer. This is supported by further spectroscopy on the anion radical complexes [(Por)Ru(CO)(L)]. The observed EPR lines are narrow, unstructured, with g values around 2. The UV-Vis-NIR spectra of the radical anions are characterised by redshifted Soret bands of reduced intensity, a weak structured band system around 600 nm and weak broad absorptions around 800 or 900 nm (see Figure 4.15). Further support comes from resonance Raman investigations on [(OEP)Ru(CO)(THF)] for which the observed Raman bands fit perfectly to those of the [(OEP)VO] radical anion. There is some evidence that if the spectroelectrochemistry is not carried out in very aprotic and unpolar solvents or traces of water are present, the radical anionic complexes are readily transformed. This has been investigated for the [(OEP)Ru(CO)(L)] system, where the use of solvents like MeOH or nitriles for the electrochemical reduction leads to altered species with unreduced porphyrin ligands (see Figure 4.15)." ... 

The ruthenium cluster dimers were dissolved in 0.1M tetra-n-butylammo-nium hexafluorophosphate (TBAH) solutions. TBAH was recrystallised from hot absolute ethanol, vacuum dried at 150 °C for 18 h, and stored under a nitrogen atmosphere. Solvents were dried over alumina in a custom solvent-purification system (Glass Contour). Spectroelectrochemistry was carried out at temperatures below 10 °C to prevent decomposition of the dimer in the (—1) and (—2) states, as the reduced dimers tend to break apart into their constituent monomeric species over prolonged periods above 10 °C. 

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