Constant Potential Electrolysis Research Articles

Synthesis and electroreduction of 2-[(8-hydroxyquinoline-5-yl)azo]benzo[c]cinnoline in DMSO–H2O (1:1) medium

2-[(8-Hydroxyquinoline-5-yl)azo]benzo[c]cinnoline (HQAB) was prepared and characterized by elemental analysis, MS, FTIR and 1H NMR techniques. The electrochemical reduction of HQAB has been investigated by cyclic voltammetry, chronoamperometry and controlled potential electrolysis at mercury pool electrode in the pH range 3.5–9.4. The number of electrons transferred in the electrode reaction, diffusion coefficients and standart rate constants were calculated. In acidic medium, cyclic voltammograms display four cathodic peaks, with the total exchange of 6 e– and 6 H+. By contrast, the reverse scan displays two anodic peaks. Constant potential electrolysis at –1.0 V and TLC analysis of the product reveals that the reduction of azo group (in the bridge) in HQAB does not stop at the hydrazo stage but goes further through the cleavage of –NH–NH– linkage to give amino compounds as the final products. The voltammograms recorded in basic medium exhibit two cathodic peaks corresponding to 4 e–, 4 H+ and two reverse anodic peaks, and thus the reduction stopped at hydrazo stage. A tentative mechanism for the reduction has been suggested.

Efficient Homogeneous Radical‐Anion Chain Reactions Initiated by Dissociative Electron Transfer to 3,3,6,6‐Tetraaryl‐1,2‐dioxanes

A series of 3,3,6,6-tetraaryl-1,2-dioxanes (TADs) have been investigated at an inert electrode by using cyclic voltammetry, constant potential electrolysis and digital simulations. The series consists of the phenyl-substituted TAD (1 a), p-methoxy-aryl TADs (1 b, 1 c) and the p-methoxy/nitro-bearing TAD (1 d). The heterogeneous electron-transfer (ET) reduction is dissociative, causing rupture of the oxygen-oxygen bond, which generates a distonic radical-anion that reacts competitively either by beta-scission fragmentation or ET. Fragmentation of the distonic radical anion yields an alkene, a substituted benzophenone, and a benzophenone radical anion. The benzophenone radical-anion propagates an efficient homogeneous ET-fragmentation chain reaction that accounts for the potential dependence of the product ratios and the low charge consumption observed in the controlled potential electrolysis experiments. Digital simulation of the experimental cyclic voltammograms allowed for estimates of the rate constants of the heterogeneous ET to the O--O bond, and for the rate constants for the beta-scission fragmentation of the distonic radical-anions. Density functional theory calculations corroborate the differences in the heterogeneous kinetics of the initial dissociative ET. The endoperoxides 1 a-1 c react predominantly by a concerted dissociative ET mechanism, although the data suggests a stepwise dissociative pathway is also competitive. Bearing a nitro-aryl substituent, 1 d provides a rare example of an endoperoxide that proceeds by a stepwise dissociative ET mechanism. Irrespective of the initial mechanistic details, we find a propagating radical-anion cycle is a general mechanistic feature.

Synthesis and electropolymerization of the phthaocyanines with 4-(2,5-di-2-thiophen-2-yl-pyrrol-1-yl) substituents

Abstract Novel tetrakis (4-(2,5-di-2-thiophen-2-yl-pyrrol-1-yl)) substituted metal-free (H 2 Pc-SNS) and zinc phthalocyanine (ZnPc-SNS) complexes were synthesized and characterized by elemental analysis, Fourier Transform Infrared (FTIR) and UV–vis spectroscopies. The solution redox properties of these complexes were also studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane (DCM) solution containing 0.1 M tetrabutylammonium perchlorate (TBAP) on platinum electrode. Both of the complexes showed two reversible reduction peaks having ligand-based character and one irreversible oxidation peak. Also, the electrochemical polymerization of these newly synthesized complexes were performed in DCM/TBAP solvent/electrolyte couple. Insoluble turquoise green and black films were deposited on the electrode surface both during repetitive cycling and constant potential electrolysis of H 2 Pc-SNS and ZnPc-SNS, respectively. Resulting polymer films, P(H 2 Pc-SNS) and P(ZnPc-SNS), were characterized by UV–vis and FTIR spectroscopic techniques and their electrochemical behavior was investigated utilizing CV. In situ spectroelectrochemical investigations revealed that both P(H 2 Pc-SNS) and P(ZnPc-SNS) films can be reversibly cycled and exhibit electrochromic behavior. Furthermore, the band gap of P(H 2 Pc-SNS) and P(ZnPc-SNS) were calculated as 2.38 eV and 2.25 eV, respectively from the on set of π–π * transition of the conjugated backbone. Moreover, the fluorescence property of the P(ZnPc-SNS) was investigated in dimethyl sulfoxide (DMSO) and toluene.

Linear free energy relationships of half-wave reduction potentials of ( E)-4-aryl-4-oxo-2-butenoic acids

Half-wave reduction potentials of a set of twelve ( E)-4-aryl-4-oxo-2-butenoic acids obtained by direct current polarography in methanol are reported. E 1/2 is correlated with Hammett sigma values as well as with values of frontier molecular orbitals calculated at a semiempirical molecular orbital level. Constant potential electrolysis of a representative compound shows that the first polarographic wave corresponds to one-electron reduction. The isolation of the product proves reduction of the activated double bond.

Electrochemical Oxidation of Ethanol Using Heterobimetallic Complexes as an Approach to DEFC Catalysts

Direct ethanol fuel cells (DEFCs) are an attractive alternative to their methanol analogues. A series of Ru/Pt, Ru/Pd and Ru/Au complexes was studied to determine the electrocatalytic activity of these complexes for the oxidation of ethanol. Cyclic voltammetry was performed to establish the affinity of these complexes towards ethanol oxidation. Constant potential (bulk) electrolysis was carried out and the liquid products of oxidation were identified and quantified by gas chromatography. Headspace gas samples were collected in a modified airfree cell and analyzed using a Fourier transform infrared spectrometer.

A comparative study of electrochemical reduction of isatin and its synthesized Schiff bases at HMDE

The electrochemical behaviour of a series of Schiff base i.e. 3-[5-phenylpyrazol-3-ylimino]indol-2-ones (IIa-e) synthesized by the reaction of various 5-substituted isatins with 3-amino-5-phenyl-pyrazole has been investigated and compared with corresponding isatin in dimethylformamide in 0·1 M LiCl using cyclic voltammetry at Hanging Mercury Drop Electrode. All synthesized Schiff bases exhibit a single irreversible two-electron reduction wave in contrast with the two discrete one-electron transfer reduction waves observed for isatin in this medium. Observation of a well-developed single reduction wave can be attributed to the higher basicity of the nitrogen species of the imine bond of Schiff bases, making proton abstraction as well as second electron transfer both rapid. The compounds are subjected to constant potential preparative electrolysis. The products are identified as secondary amines by spectroscopic methods. A mechanism for the electro-reduction process has been proposed. Kinetic parameters have also been calculated.

Electrodeposition of Palladium–Copper Films from 1-Ethyl-3-methylimidazolium Chloride–Tetrafluoroborate Ionic Liquid on Indium Tin Oxide Electrodes

The electrodeposition of palladium-copper alloys in 1-ethyl-3-methylimidazolium chloride–tetrafluoroborate ionic liquid containing excess chloride ions was studied on indium tin oxide (ITO) coated glass electrodes at . Cyclic voltammogrammetric results indicate that the thermodynamic deposition potential of copper is more negative than that of palladium. The presence of palladium(II) reduces the overpotential required for the deposition of copper. In addition, underpotential deposition of copper on the palladium electrode was observed. In contrast, the presence of copper(II) increases the overpotential required for the deposition of palladium. Palladium–copper coatings were prepared on the ITO electrode by constant potential electrolysis. Scanning electron microscopy results indicate that the deposits had nodular morphologies. Calculations from X-ray powder diffraction data show that the crystal size of the deposit decreased with increasing deposition overpotential. The prepared palladium–copper coatings adhered well on the ITO substrates and showed a good electrocatalytic capability for the electro-oxidation of ethanol in alkaline solution.

Determination of Hg 2+ on poly(vinylferrocenium) (PVF +)-modified platinum electrode

A new surface based on poly(vinylferrocenium) (PVF +)-modified platinum electrode was developed for determination of Hg 2+ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF +ClO 4 −. Cl − ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg 2+ solution. Hg 2+ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl −. Detection of Hg 2+ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg 2+. Mercury ions as low as 5 × 10 −10 M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10 −6 M concentration ( n = 6). Interferences of Ag +, Pb 2+ and Fe 3+ ions were also studied at two different concentration ratios with respect to Hg 2+. The developed electrode was applied to the determination of Hg 2+ in water samples.

Photo-electrochemical degradation of some chlorinated organic compounds on n-TiO 2 electrode

The electrolysis of some chlorinated organic compounds such as chloroacetic acids, chloromethanes and chloroethenes were carried out on a photo-irradiated n-TiO 2 electrode applied a constant potential, 1.0 V vs. Ag/AgCl, and the alternated pulse potentials of +1.0 V and various negative potentials, −1.0, −1.2 and −1.4 V vs. Ag/AgCl in 0.1 mol dm −3 Na 2SO 4 solutions saturated with oxygen or with nitrogen. These compounds were degraded on the n-TiO 2 electrode by the photo-electrolysis and mineralized to carbon dioxide, carbon monoxide and chloride ion. When the alternated pulse potentials were applied, the mineralization yields were increased for these compounds, especially for trichloroacetic acid and carbon tetrachloride, both of which were comparatively stable to the degradation in the constant potential electrolysis. The presence of oxygen in the solution was effective for the mineralization of these compounds, while little effective for that of trichloroacetic acid and of carbon tetrachloride.

A new conducting polymer bearing 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene (BODIPY) subunit: Synthesis and characterization

A new monomer system based on thiophene, pyrrole and 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene dye (SNS-BODIPY) was synthesized and its corresponding polymer (PSNS-BODIPY) was obtained via repetitive cycling or constant potential electrolysis in 0.1 M tetrabutylammonium hexafluorophosphate dissolved in dichloromethane. The PSNS-BODIPY film has very stable and well-defined reversible redox couples during p-doping process. Multi-electrochromic polymer film has a band gap of 2.9 eV with two absorption bands in its neutral state at 351 and 525 nm, attributed to the polymer backbone and BODIPY subunits, respectively. The percentage transmittance changes between both states (neutral and oxidized) were found as 12.1% for 351 nm and 17.7% for 525 nm in the visible region as well as 46.2% for 1050 nm in the near-infrared region. Beyond the robustness, the PSNS-BODIPY film has high redox stability (retaining 53.3% of its electroactivity at 351 nm after 2000 switching) with a low response time of 1.0 s.

Seed-mediated electrochemical growth of gold nanostructures on indium tin oxide thin films

Abstract Two-dimensional gold nanostructures (Au NSs) were fabricated on amine-terminated indium tin oxide (ITO) thin films using constant potential electrolysis. By controlling the deposition time and by choosing the appropriate ITO surface, Au NSs with different shapes were generated. When Au NSs were formed directly on aminosilane-modified ITO, the surface roughness of the interface was largely enhanced. Modification of such Au NSs with n -tetradecanethiol resulted in a highly hydrophobic interface with a water contact angle of 144°. Aminosilane-modified ITO films further modified with colloidal Au seeds before electrochemical Au NSs formation demonstrated interesting optical properties. Depending on the deposition time, surface colors ranging from pale pink to beatgold-like were observed. The optical properties and the chemical stability of the interfaces were characterized using UV–vis absorption spectroscopy. Well-defined localized surface plasmon resonance signals were recorded on Au-seeded interfaces with λ max = 675 ± 2 nm (deposition time 180 s). The prepared interfaces exhibited long-term stability in various solvents and responded linearly to changes in the corresponding refractive indices.

Electrodeposition of Aluminum from AlCl 3/Et 3NHCl Ionic Liquids

Aluminum was successfully electrodeposited on Al electrodes from aluminum chloride (AlCl 3)/triethylamine hydrochloride (Et 3NHCl) ionic liquids by the constant potential electrolysis. Electrical conductivities of AlCl 3/Et 3NHCl ionic liquids were measured as a function of the temperature and composition. The nucleation processes and the influence of experimental conditions on the current efficiency and surface morphology of aluminum electrodeposits were studied on Al electrodes from 2:1 molar ratio AlCl 3/Et 3NHCl ionic liquid. The electrical conductivities of ionic liquids increased as the electrolyte temperature increased, following the Arrhenius behavior. Analyses of the chronoamperograms indicated that the deposition process of aluminum on Al substrates was controlled by instantaneous nucleation with diffusion-controlled growth. Constant potential deposition experiments showed that the electrodeposits obtained on Al electrodes were dense, continuous, and well adherent, and the current efficiency was 73% at −2.4 V( vs Pt) for 20 min electrolysis at room temperature. The purity of aluminum electrodeposits on Al electrodes was above 96% ( w).

Influence of nitrate concentration on its electrochemical reduction on tin cathode: Identification of reaction intermediates

The influence of the concentration of nitrate in the range between 100 and 62,000 mg L −1 NaNO 3 in NaCl solutions was studied under constant potential electrolysis at −2.8 V vs. Ag/AgCl. The rate of the reduction follows Langmuir–Hinshelwood kinetics, according to which zero order kinetics is followed at concentrations higher than 0.3 M whereas first order at lower concentrations. The selectivity to nitrogen increases from 70 to 83% as the concentration of nitrate increases from 100 to 1500 mg L −1 and it remains almost constant for higher nitrate concentrations, whereas that of ammonia exhibits the opposite trend decreasing from 25 to 11%. The % Faradaic Efficiency (%FE) increased with the increase of the concentration of nitrate from 25% at 0.1 M to 78% at 1 M when 95% of nitrate was reduced in both cases. At high concentrations of nitrate, hyponitrite and hydroxylamine were detected as intermediates of the reduction and a reaction scheme which is in agreement with the experimental results has been proposed. The hydrogen evolution in our conditions probably takes place through the discharge of the cation of the supporting electrolyte instead of the Volmer–Tafel mechanism and the reduction of nitrate proceeds through electrochemical hydrogenation.

Electrochemical polymerization of 9-fluorenecarboxylic acid and its electrochromic device application

Poly(9-fluorenecarboxylic acid) (PFCA) was synthesized by electrochemical oxidation of 9-fluorenecarboxylic acid (FCA) using a mixture of nitromethane and boron trifluoride diethyl etherate as the solvent and tetrabutylammonium tetrafluoroborate as the supporting electrolyte. An insoluble and conducting brownish-orange film was deposited on the electrode surface, both during repetitive cycling and constant potential electrolysis at 1.15 V. Characterization of the polymer film has been carried out using Fourier Transform Infrared spectroscopy technique and thermal behavior was studied via thermal gravimetric analysis. Structural analysis showed that the polymerization of FCA occurred at 2,7-position. Spectroelectrochemical behavior of the polymer film on indium tin oxide working electrode was studied by recording the electronic absorption spectra, in-situ, in monomer-free electrolytic solution at different potentials and it is found that the PFCA film can be reversibly cycled between 0.0 V and 1.2 V. Furthermore, a dual type electrochromic device based on PFCA was constructed and its spectroelectrochemical properties were investigated. The electrochromic device exhibits color change from transparent to dark blue with a good open circuit memory.

Electrochemical costripping models and mutual interferences of mutli-transition metal systems on the surface of boron-doped diamond

Electrochemical behaviors of electrodeposition stripping of some transition metals, such as Ag, Cu, Pb, Sn, and Cd were investigated on boron-doped diamond (BDD) film with differential pulse anodic stripping voltammetry (DPASV). The results show that the metal costripping process on the surface of BDD is influenced by deposition potential of transition metals, potential of hydrogen evolution reaction, mutual interferences between two transition metals, and so on. Electrochemical costripping models and mutual interferences of binary transition metals are proposed. (i) When the hydrogen evolution potential is higher or lower than the deposition potential of two transition metals, the metals do not form alloys and compound the cathode ions in the solution, and the costripping process conforms to metal 1 stripping-metal 2 stripping. (ii) When the hydrogen evolution potential is between the deposition potential of two transition metals, the metals do not form alloys and compound the cathode ions in the solution, and the costripping process conforms to metal 1 stripping-hydrogen evolution-metal 2 stripping. (iii) When two transition metals form alloys, the costripping process conforms to metal 1 stripping-alloy striping-metal 2 stripping. (iv) When the hydrogen evolution potential is between deposition potential of two transition metals, and transition metal 2 is complexed with one kind of cathode ion in the solution, the costripping process conforms to metal 1 stripping-hydrogen evolution-metal 2 complex formation-metal 2 stripping. Moreover, the electrochemical-costripping model of two transition metals in a solution with three or more transition metals, is similar to that in the binary system. It is also found that various metals electrodeposited on BDD film in the form of single metal or alloy can be completely stripped away by the constant-potential electrolysis technique at 2.8 V for 10 s.

Electrodeposition of Sb-Te Alloy in AlCl<SUB>3</SUB>-NaCl-KCl Molten Salt

The Electrodeposition of Sb-Te alloy was carried out in AlCl 3 -NaCl-KCl molten salt containing SbCl 3 and TeCl 4 at 423 K by constant potential electrolysis. The voltammogram on a glassy carbon (GC) electrode in a melt containing 1.0 x 10 -2 kmol m -3 SbCl 3 and 1.0 x 10 -2 kmol/m 3 TeCl 4 revealed the cathodic current waves at 1.5, 1.1, and 0.9 V vs. Al/Al(III). A stable Sb-Te alloy deposit was obtained at 0.85 V in the melt containing SbCl 3 and TeCl 4 . At the higher concentration ratio of the Sb(III) to (Sb(III) + Te(IV)), a good linear relation was found between the atomic ratio of Sb in the deposit and the concentration ratio of Sb (III) in the melt. The Sb-Te alloy deposit of atomic ratio of 38: 62% which was assume to be suitable for a thermoelectric device was obtained with the molten salt containing 7.0 x 10 -3 kmol/m 3 SbCl 3 and 1.0 x 10 -2 kmol/m 3 TeCl 4 . The XRD pattern of the deposit corresponds to that of Sb 2 Te 3 intermetallic compound. The deposit had homogeneous disk-like granule with the disk size of about 10 μm.

Investigation on electrochemical reduction process of Nb 2O 5 powder in molten CaCl 2 with metallic cavity electrode

The direct electrochemical reduction process of Nb 2O 5 powder was investigated by cyclic voltammetry and constant potential electrolysis with a novel metallic cavity electrode in molten calcium chloride at 850 °C. The products of both constant potential and constant voltage electrolysis were characterized by XRD, SEM and EDX. CaNb 2O 6 was formed upon addition of solid Nb 2O 5 into molten CaCl 2 when CaO was present. During the electrolysis solid Nb 2O 5 was reduced to various niobium oxides of lower oxidation states, including some composite oxides, and then was converted completely to metallic niobium near −0.35 V ( vs. Ag/AgCl), which was more positive than the reduction potential of Ca 2+. Constant potential electrolysis was applied at the potentials near the reduction current peaks derived from the cyclic voltammetry curves, and cell voltages were monitored. The voltage was near 2.4 V when the oxide was metallized at −0.35 V ( vs. Ag/AgCl). Nb 2O 5 pellet could be used to prepared metallic niobium at cell voltage 2.4 V in a larger electrolysis bath filled with calcium chloride at 850 °C. The experiment results further demonstrated the direct electrochemical reduction mechanism of Nb 2O 5 powder in a molten system.

Development of single-wall carbon nanotubes modified screen-printed electrode using a ferrocene-modified cationic surfactant for amperometric glucose biosensor applications

The application of electrodeposited single-wall carbon nanotubes (SWCNT) as an immobilization matrix for the construction of amperometric glucose biosensor is described. The surface of an electrode was modified by addition of SWCNT and glucose oxidase (GOD), the latter of which was immobilized using 11-(ferrocenyl)-undecyltrimethylammonium bromide (FTMA); the formation and disruption of vesicles in FTMA was controlled by constant potential electrolysis. SWCNT has promotion effects on the direct electron transfer of GOD, which was immobilized with SWCNT. The cyclic voltammetric results indicated that direct electron transfer between the active center of immobilized GOD and the surface of the electrode occurred. The electron-transfer coefficient was 0.70 ± 0.3 and electron-transfer rate constant was evaluated to be 2.69 ± 0.03 s−1. This modified electrode was used to measure d-glucose concentration; a linear relationship between steady-state current and concentration was found over a range of 0.04–0.38 mM d-glucose, with a slope of 1.73 μA/mM, and the electrode retained 78.62% of its initial response after 50 cycles. The variation coefficient was 10.6% (n = 10) for samples with a d-glucose concentration of 0.04 mM. Even after 42 days, the residual activity of the modified electrode was over 94%, and it was still useful for determination of d-glucose.

Synthesis and electrocoating of indole–thiophene comonomer on carbon fiber microelectrode, and surface topography by AFM

5,2-Thiophenylindole(5,2 In–Th) comonomer is synthesized by means of palladium catalyzed Stille cross-coupling reaction with an aim of obtaining extensively conjugated, low oxidation potential comonomer relative to its corresponding monomer. The comonomer is characterized by UV–Visible, FTIR, and NMR spectroscopic techniques, and the resulting conjugated copolymer exhibited the properties of both polyindole and polythiophene (having low oxidation potential and high conductivity). 5,2 In–Th comonomer was electropolymerized onto carbon fiber microelectrodes. The copolymer was electrochemically coated (grafted) onto micron size carbon fiber by constant potential electrolysis and cyclic voltammetry (CV) and the resulting nanosize thin films of polymers were characterized using atomic force microscopy (AFM), and FTIR spectroscopy. The efficiency of the electrocopolymerization process on the carbon fiber surfaces under preparative constant current electrolysis and potentiodynamic conditions, was evaluated in order to ascertain the effects of copolymer thickness, dopant and morphology.

Bis‐μ‐pyrazolate‐Bridged Dinickel(II) and Dicopper(II) Complexes: An Example of Stereoelectronic Preference of Metal Ions and Stabilization of Mixed‐Valence NiIIINiII Species

AbstractNew dimeric nickel(II) and copper(II) complexes [(L)Ni(μ‐L′)]2[ClO4]2 1 and [(L)Cu(μ‐L′)]2[ClO4]2 2, [2‐[3‐(2′‐pyridyl)pyrazol‐1‐ylmethyl]pyridine (L) and 3‐(2‐pyridyl)pyrazole (HL′)] have been synthesized, structurally characterized, and their absorption, magnetic, EPR and redox properties investigated. The crystal structure of 1·MeCN reveals a planar {Ni2(μ‐L′)2}2+ core [Ni···Ni separation: 4.0765(10) Å] in which each distorted octahedral NiII ions is terminally coordinated by a tridentate ligand L and bridged by two HL′ units, in their deprotonated form. The structural analysis of 2·2MeCN reveals two five‐coordinate CuII ions, each terminally coordinated by adopting only a bidentate coordination mode of L, in which the –CH2py arm remains uncoordinated. A similar bridging [Cu···Cu separation: 3.9382(24) Å] as in 1·MeCN is observed. Thus stereoelectronic preferences of NiII and CuII are clearly revealed. Closer inspection of crystal packing diagram of 1·MeCN reveals the formation of 2‐D network structure assembled solely via C–H···π interaction [pyridyl C–H (4‐position) of pyridylpyrazole unit of L and π cloud of pyridine of bridging deprotonated L′ unit]. In 2·2MeCN, however, π···π interactions between uncoordinated pyridyl arms are observed. Variable‐temperature magnetic studies on both complexes indicate the existence of strong antiferromagnetic coupling between the two metal ions (singlet‐triplet energy separation, J = –20 cm–1 for 1 and –200 cm–1 for 2). When investigated by cyclic voltammetry complex 1 displays two quasi‐reversible electron‐transfer reactions at E1/2 = 1.36 V (ΔEp = 110 mV) and 1.79 V (ΔEp = 120 mV) vs. SCE, due to NiIIINiII/NiII2 and NiIII2/NiIIINiII redox processes, respectively. Constant potential electrolysis at 1.50 V vs. SCE leads to the generation of dark green mixed‐valence NiIIINiII species, which is stable enough to be subjected to characterization by UV/Vis and EPR spectroscopy. Compound 2 exhibits only irreversible reductions (cathodic peak potential, Epc = –0.28 V and –0.50 V vs. SCE).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)