Quasi-reversible One-electron Process Research Articles

Mono- and di-(2,3,5,6-tetrafluoro-4-N,N-dimethylaminophenyl) meso-tetraarylporphyrins: Synthesis, spectral, structural and electrochemical studies

A new series of mono-/di-aminated meso-tetraarylporphyrins has been synthesized and characterized by conventional spectroscopic methods. Crystal structure analysis shows that interactions involving halogens are the major contributors, and the relative contributions are 56% and 53% respectively for MB2c and MB3c. All the compounds were electrochemically analyzed under different reaction conditions and showed a positive shift in the reduction and oxidation potentials. The HOMO–LUMO energy gap was altered with respect to the nature of the supporting electrolyte and reference electrodes used. The linear behavior of Randles-Sevcik plots indicate that the redox processes are diffusion controlled; the first reduction/oxidation is a reversible one-electron step whereas the second reduction/oxidation is a quasi-reversible one-electron process. Results also reveal that the mono-aminated porphyrins are more electron deficient than non-aminated and di-aminated porphyrins.

Synthesis, characterization and coordinating properties of an NNS donor system, 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone (HMPzPyr), and it's cobalt(III), nickel(II) and copper(II) complexes

The ligational behaviour of 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone has been demonstrated by isolation and characterisation of its complexes with cobalt(III), nickel(II) and copper(II) with different counterions. Magnetic and spectral features indicate [Co(MPzPyr) 2 ]X (X = Cl, Br, NO 3 , ClO 4 or BF 4 ) as the diamagnetic octahedral species with the ligand in the deprotonated thiol form, while [Ni(HMPzPyr) 2 ]X 2 (X = Cl, Br or NO 3 ) is proposed as octahedral complex with the ligand in the neutral thione form. However, at pH ∼6, nickel(II) salts afford octahedral bis-nickel(II) complex, Ni(MPzPyr) 2 , while copper(II) salts in acetonitrile medium give Cu(MPzPyr)X (X = Cl, Br or NO 3 ) with the deprotonated ligand. IR spectra indicate that the pyrazolyl ring nitrogen ( 2 N), the azomethine nitrogen and the sulphur atom are the points of attachment with the metal ion in all these complex species. The cyclovoltammetric study of copper(II) complexes reveals the quasi-reversible one-electron process (Cu II → Cu I ), where the EPR data confirm the presence of d x2―y2 ground state of these complexes.

Electrochemical recognition of analytes using quaternary ammonium binaphthyl salts.

The electrooxidation of quaternary ammonium binaphthyl salts is shown to proceed by a quasi-reversible one-electron process. The oxidation of an aza-crown ether substituted binaphthyl salt is affected by the presence of lithium and sodium ions in solution and there is shown to be a linear relationship between the limiting current for the process and the concentration of Li+ and Na+. The electrochemistry of the binaphthyl salt is also shown to be affected by the addition of organic cations to the solution, showing that these receptors could form the basis of analytical devices which could be made specific to a range of analytes.

Enforcing geometrical constraints on metal complexes using biphenyl-based ligands: spontaneous reduction of copper(II) by sulfur-containing ligands

Two biphenyl-based N2S2 ligands, 2,2′-bis-(4-methylimidazol-5-yl)methylsulfanyl)biphenyl (N2S2-mim) and 2,2′-bis(2-pyridylmethylsulfanyl)biphenyl (N2S2-mpy), have been synthesized and their complexation with copper(II) precursors studied. In order to assess whether the biphenyl ring is influencing the geometry around the copper atom, the NS ligand 1-methyl-4-(2-pyridylmethylsulfanyl)benzene (NS-mpy) and its copper complexes were prepared. The N4 ligand 2,2′-bis-(2-pyridylmethylamino)biphenyl (N4-mpy) in which the sulfurs have been replaced by nitrogens also was prepared. Treatment of N4-mpy with copper(II) salts led to isolation of copper(II) complexes with the formula [Cu(N4-mpy)]X2 where X = ClO4 or BF4. These complexes were analysed by a combination of elemental analysis, IR spectroscopy, FAB MS and electrochemistry. Likewise, treatment of NS-mpy with copper(II) salts led to isolation of the copper(II) complexes [Cu(NS-mpy)2][ClO4]2 or [Cu(NS-mpy)2][BF4]2. In comparison to the results found for ligands N4-mpy and NS-mpy, treatment of N2S2-mim or N2S2-mpy with [Cu(H2O)6][ClO4]2 or [Cu(H2O)6][BF4]2 in MeOH led to spontaneous reduction to form the copper(I) complexes [Cu(N2S2-mim)]ClO4 [Cu(N2S2-mim)]BF4, [Cu(N2S2-mpy)]ClO4 and [Cu(N2S2-mpy)]BF4. The formulation of these complexes as copper(I) species was confirmed by analytical methods, and for [Cu(N2S2-mpy)]ClO4·MeCN by X-ray crystallography. The copper(I) ion is in a distorted tetrahedral environment ligated by two nitrogens and two thioethers from the ligand. Cyclic voltammetry shows [Cu(N2S2-mpy)]ClO4, [Cu(N4-mpy)][ClO4]2 and [Cu(NS-mpy)2][ClO4]2 undergo quasi-reversible one-electron processes with Eo′ is +0.77, +0.21 and +0.53 V vs. SCE.

Redox Potentials of Bromo- and Chloro(phthalocyaninato)bismuth(III) Complexes

Abstract The redox potentials of the titled complexes, [Bi(pc)X] (pc2− = phthalocyaninate, C32H16N82−, and X = Cl− and Br−), in N,N-dimethylformamide solutions have been determined by cyclic voltammetry for the first time as phthalocyanine complexes of group-15 elements. The voltammograms of [Bi(pc)Cl] consisted of one oxidation (E1/2 = 0.36 V vs. ferrocene/ferricinium+) and two reduction couples (ca. −1.2 and ca. −1.0 V), each of which was a quasi-reversible one-electron process. The voltammograms of [Bi(pc)Br] were quite similar to those obtained with [Bi(pc)Cl], with the exception of the appearance of an additional irreversible anodic peak at 0.30 V, which could be attributable to the oxidation of non-ligand bromide, suggesting the dissociation of [Bi(pc)Br] into [Bi(pc)]+ and Br− in DMF. This is the first case in which [M(pc)X]-type (M = trivalent metal) complex dissociated into [M(pc)]+ and X− in solution.

Voltammetric studies on substituted 2-arylazoanthraquinones in non-aqueous medium

Substituted 2-arylazo-anthraquinones are electrochemically studied in benzonitrile at an rde. These compounds are oxidized in a single quasi-reversible two electron wave or in a two quasi-reversible one-electron processes depending on the nature of substituent, leading to the formation of the dication followed by proton removal to form the monocation which can be stabilized through its combination with the perchlorate anion from the supporting electrolyte. The reduction process occurs in three successive electron transfer processes. The coloumetric measurements indicated two-electrons for the first step and one-electron for each of the second and third steps. The azo moiety is reduced in the first step to the dianion which accepts two protons from the solvent to give the corresponding hydrazo. The second and third electron transfers were assigned to the reduction of the quinone moiety to form the corresponding radical-anion and dianion.

Electrochemical and ESR studies of [Fe(terpy)2]2+ and [Ru(terpy)2]2+ and their reduction products

The cyclic voltammetry of [Fe(terpy)2]2+ and [Ru(terpy)2]2+ and the frozen solution ESR spectra of the one-, two- and three-electron reduction products for both are reported. A total of four redox steps are resolved for both complexes. The first two are reversible one-electron processes, the third is a quasi-reversible one-electron process and the fourth step apparently involves an ECE mechanism. Only the one- and two-electron reduction products are chemically stable on a long time scale. However, the ESR spectra for all products can be described by an S=1/2 spin Hamiltonian. These results are interpreted to imply that the redox orbitals are single chelate ring types.

Electrochemical and ESR studies of [Fe(terpy) 2] 2+ and [Ru(terpy) 2] 2+ and their reduction products

The cyclic voltammetry of [Fe(terpy) 2] 2+ and [Ru(terpy) 2] 2+ and the frozen solution ESR spectra of the one-, two- and three-electron reduction products for both are reported. A total of four redox steps are resolved for both complexes. The first two are reversible one-electron processes, the third is a quasi-reversible one-electron process and the fourth step apparently involves an ECE mechanism. Only the one- and two-electron reduction products are chemically stable on a long time scale. However, the ESR spectra for all products can be described by an S=1/2 spin Hamiltonian. These results are interpreted to imply that the redox orbitals are single chelate ring types.

Novel method for the investigation of the electrochemistry of metalloproteins: cytochrome c

The d.c. and a.c. cyclic voltammetries of horse heart ferricytochrome c have been investigated and it is shown that in the presence of 4,4′-bipyridyl, the electrochemistry corresponds to a quasi-reversible one-electron process, from which an E° value of +0·25 V vs. normal hydrogen electrode can be derived.