Electrochemical reduction of zinc complexes from glycinate solutions

Kinetics of electrochemical reduction of zinc(II) complexes is studied in a wide range of solution pH using the polarization measurements and chronopotentiometry. Adsorption of glycinate ions on zinc electrode and complexing of zinc(II) with glycine are studied using the ¹³C NMR method. Based on the experimental data, the electrochemical behavior of zinc(II)–glycine–water system is considered.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 228–231.Original Russian Text Copyright © 2005 by Berezin, Sagdeev, Gudin, Roev, Mezhevich.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Electrochemical behaviour of Cu-NTA complexes

The deposition of copper was found to involve adsorbed monovalent copper which follows nonactivated Temkin isotherm. The presence of nitrilotriacetic acid stabilises it and the second electron transfer is slow.     

Electrochemical synthesis and properties of δ-fluoroacyl and δ-perfluoroalkyl transition metal complexes

The electrochemical synthesis of δ-fluoroacyl complexes [M]-δ-COR_f(M=C₅H₅(CO)₃W or (CO)₅Mn; R_f=CF₃ or C₄F₉) was performed according to two procedures: (1) the preliminary electrochemical synthesis of [M]⁻ from [M]₂ followed by reaction with a fluorine-containing compound and (2) the electrochemical synthesis of [M]⁻ in the presence of a fluorine-containing compound. Trifluoroacetic anhydride was demonstrated to be the best acylating agent in these reactions. The electrochemical properties of the resulting complexes were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 373–375, February, 2000.     

Proton reduction catalysis by manganese vinylidene and allenylidene complexes

The present paper reports the unprecedented observation of a catalytic electrochemical proton reduction based on metallocumulene complexes. Manganese phenylvinylidene (η⁵-C₅H₅)(CO)(PPh₃)MnCC(H)Ph (1) and diphenylallenylidene (η⁵-C₅H₅)(CO)₂MnCCCPh₂ (3) are shown to catalyze the reduction of protons from HBF₄ into dihydrogen in CH₂Cl₂ or CH₃CN media at −1.60 and −0.84 V (in CH₃CN) vs. Fc, respectively. The working potential for 3 (−0.84 V vs. Fc in CH₃CN) is the lowest reported to date for protonic acids reduction in non-aqueous media. The similar catalytic cycles disclosed here include the protonation of 1, 3 into the carbyne cations [(η⁵-C₅H₅)(CO)(PPh₃)MnC-CH₂Ph]BF₄ ([2]BF₄), [(η⁵-C₅H₅)(CO)₂MnC-CHCPh₂]BF₄ ([4]BF₄) followed by their reduction to the corresponding 19-electron radicals 2, 4, respectively. Both carbyne radicals undergo a rapid homolytic cleavage of the C_β-H bond generating an H-radical producing molecular hydrogen with concomitant recovery of the neutral metallocumulenes thereby completing a catalytic cycle.     

Electrochemical behaviour of azaferrocenes and reactivity of azaferrocenium cations

The electrooxidation of azaferrocene (AF) and 2,5-dimethylazaferrocene (DMAF) has been investigated in several solvents and under various conditions of basicity and nucleophilicity, by cyclic voltammetry at scan rates ranging between 1 and 500 V s⁻¹. The kinetics of the AF⁺ cation decomposition have been found to be first order (vs. the substrate), and strongly dependent on both the solvent and the possible presence of a base. The results tend to demonstrate that the decomposition of AF⁺ cations is more probably associated with a deprotonation reaction than with a nucleophilic attack.     

Electrochemical behaviour of alkaline copper complexes

A search for non-cyanide plating baths for copper resulted in the development of alkaline copper complex baths containing trisodium citrate [TSC] and triethanolamine [TEA]. Voltammetric studies were carried out on platinum to understand the electrochemical behaviour of these complexes. In TSC solutions, the deposition of copper involves the slow formation of a monovalent species. Adsorption of this species obeys Langmuir isotherm. In TEA solutions the deposition involves the formation of monovalent ions obeying the non-activated Temkin isotherm. Conversion of divalent to monovalent copper is also slow. In TEA and TSC alkaline copper solutions, the predominant species that undergo stepwise reduction contain only TEA ligands.     

Electrochemical synthesis for new thiosemicarbazide complexes,spectroscopy, cyclic voltammetry,structural properties,and in silico study

A new thiosemicarbazide derivative ligand (HDCTS) was prepared from the reaction between 2,4‐dinitrophenylhydrazine and 4‐chlorophenyl isothiocyanate. Co(II) and Cu(II) complexes were synthesized from HDCTS derivative by electrochemical method to reach preferable yield in a safe environment. The new complexes as well as the original ligand were fully characterized to establish their chemical formulae. The spectral (infrared, Raman, mass, and ultraviolet–visible), analytical (elemental, thermogravimetric analysis [TGA], and cyclic voltammetry), and conformational techniques were implemented for characterization. According to spectral data and magnetic moments, the octahedral arrangement was proposed around metals through mono‐negative bidentate mode of bonding. TGA discriminates and quantitatively evaluates the presence of water molecules within two complexes. Electrochemical study was interested for all new compounds and suggests the electrode couples to be close for quasi‐reversible behavior. Elaborated conformational study was displayed to extract significant characteristics, which assert firstly on the mode of bonding inside the complexes. The perfect distribution of NH and CS groups inside the optimized structures facilitates their coordination as spectrally proposed. Crystal explorer program was used to investigate the degree of contact between molecules inside crystal packing systems. Effective contribution in surface contact feature was noticed from O and Cl atoms. A certified in silico study concerning the docking feature of new compounds against effective proteins in allergy and inflammation diseases was done. According to data exported, a promising anti‐allergic or anti‐inflammatory efficiency is expected strongly from Cu(II)–DCTS complex.     

Electrochemical behaviour of a lead electrode in phosphoric acid

 A lead electrode was studied in 6 and 12 M H₃PO₄. Oxidation of a freshly polished electrode occurred in the −0.5 to −0.3 V vs. SCE range, and led to PbHPO₄ growth on the electrode surface. The dissolution of this layer by electrochemical reduction occurred between −0.5 and −0.7 V. The influence of temperature (20 °C and 65 °C) was investigated and showed that the anodic and the cathodic peaks were increasing, and more markedly for the 12 M H₃PO₄. The ratio Q _cathodic/Q _anodic (Q=electrical charge flowing through the electrode) was equal or close to the unity at 20 °C and decreased as the temperature was increased. The influence of Cl⁻, Br⁻ and I⁻ ions was also evaluated. The addition of Cl⁻ and Br⁻ predominantly led to Pb₅(PO₄)₃Cl and Pb₅(PO₄)₃Br, respectively, while I⁻ led to a mixture of PbI₂ and PbHPO₄. Received: 18 July 1999 / Accepted: 2 November 1999     

Transition metal complexes of acetamidomalondihydroxamate: synthesis,spectral, thermal and electrochemical studies

Acetamidomalondihydroxamate (K₂AcAMDH) and its manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized and characterized by elemental analysis, UV–VIS, IR and magnetic susceptibility. The pK _a1 and pK _a2 values of the dihydroxamic acid in aqueous solution were found to be 8.0?±?0.1 and 9.7?±?0.1. The dihydroxamate anion AcAMDH behaves as a tetradentate bridging ligand through both hydroxamate groups, forming complexes with a metal to ligand ratio of 1?:?1 in the solid state. The FTIR spectra and thermal decompositions of the ligand and its metal complexes were recorded. The redox behavior of the complexes was investigated in aqueous solution by square wave voltammetry and cyclic voltammetry at neutral pH. In contrast to the solid state, in solution the copper(II) and zinc(II) ions form stable complex species with a metal to ligand ratio of 1?:?2. The iron(II) and nickel(II) complexes show a two-electron irreversible reduction behavior, while the copper(II) and zinc(II) complexes undergo reversible electrode reactions. The stability constants of the complexes were determined by square wave voltammetry.     

Electrochemical behaviour of thiol-derivatised zinc (II) phthalocyanine complexes and their self-immobilised films at gold electrodes

Electrochemical properties of novel, peripherally substituted zinc phthalocyanine complex, octa(4-methylphenylthio-) phthalocyaninatozinc(II) [ZnPc(SC₆H₄CH₃)₈] (1a) in DMF solution are presented. This complex showed five quasi-reversible/reversible, diffusion-controlled redox couples. Solution voltammetry of 1a showed little contrast with that of its alkythiol-derivative, octabutylthiophthalocyaninatozinc(II) [ZnPc(SC₄H₉)₈] (1b) in that both thiol-substituents tend to show electron-withdrawing influence on the phthalocyanine ligands; complex 1a showing easier reduction and more difficult to oxidation when compared to 1b and other alkyl derivatives. The voltammetric features of the solid ultrathin films of 1a and 1b, immobilized on gold electrodes via the self-assembling technique, are also presented. Interestingly, the self-assembled films are stable and reproducible and provide good suppression to the following Faradaic processes; gold surface oxidation, solution ion species and underpotential deposition (UPD) of copper.     

Electrochemical and spectral study of intramolecular charge transfer in dinuclear and polynuclear ladder complexes

The potentials of electrochemical oxidation and reduction of the polynuclear ladder complexes Cp(CO)LM-η ¹, η⁵-C₅H₄Mn(CO)₂L (M = Fe or W(CO); L = PPh₃ or CO), μ-(C≡ C)[C₅H₄(CO)₂Fe-η¹, η⁵-C₅H₄Mn(CO)₃]₂, and MeSi[C₅H₄(CO)₂Fe-η¹, η⁵-C₅H₄Mn(CO)₃]₃ were measured, and the mechanism of these processes is proposed. The change in the electron density at the atom of one metal (Fe or W) is transferred along the σ-and σ-bond chain in the cyclopentadienyl bridge to the atom of another metal (Mn) and, on the contrary, the perturbing effect of the substituent is somewhat weakened. Published In Russian In Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, Pp. 761–765, May, 2006.     

Spectral, thermal, electrochemical and analytical studies on Cd(II) and Hg(II) thiosemicarbazone complexes

The coordination characteristic of the investigated thiosemicarbazones towards hazard pollutants, Cd(II) and Hg(II), becomes the first goal. Their complexes have been studied by microanalysis, thermal, electrochemical and spectral (electronic, IR and MS) studies. The substitutent (salicylaldehyde, acetophenone, benzophenone, o-hydroxy-p-methoxybenzophenone or diacetylmonoxime) plays an important role in the complex formation. The coordination sites were the S for thiosemicarbazide (HTS); NN for benzophenone thiosemicarbazone (HBTS); NS for acetophenone thiosemicarbazone (HATS) and salicylaldehyde thiosemicarbazone (H(2)STS); NNS or NSO for diacetylmonoxime thiosemicarbazone (H(2)DMTS). The stability constants of Hg(II) complexes were higher than Cd(II). The kinetic and thermodynamic parameters for the different thermal decomposition steps in the complexes have been evaluated. The activation energy values of the first step ordered the complexes as: [Cd(H(2)STS)Cl(2)]H(2)O>[Cd(H(2)DAMTS)Cl(2)]>[Cd(HBTS)(2)Cl(2)]2H(2)O>[Cd(HATS)(2)Cl(2)]. The CV of [Cd(H(2)STS)Cl(2)]H(2)O and [Hg(HBTS)Cl(2)] were recorded. The use of H(2)DMTS as a new reagent for the separation and determination of Cd(II) ions from water and some synthetic samples using flotation technique is aimed to be discussed.     

Electrochemical behavior of dopamine at a quercetin-SAM-modified gold electrode and analytical application

A stable quercetin–thioglycolic acid-modified gold electrode (Qu–TCA/Au) was prepared as a self-assembled monolayer (SAM) and its electrochemical behavior was investigated by electrochemical methods. In 0.05-M phosphate buffer solution (pH 7.0) quercetin exhibits quasi-reversible signals at the Qu–TCA/Au electrode. The stability of the quercetin-modified gold electrode is very good. The quercetin self-assembled monolayer is an effective mediator for the oxidation of dopamine, which was investigated by cyclic voltammetry and differential pulse voltammetry. Ascorbic acid does not interfere with determination of dopamine at an electrode modified with a mixture of quercetin–thioglycolic acid and quercetin–11-mercaptoundecanoic acid. This modification allows dopamine to be determined in the presence of ascorbic acid in the range from 3×10^–5 to 3×10^–4 M. The detection limit is 1×10^–6 M. Scanning electrochemical microscopy (SECM) was employed to study the electrochemical performances of the modified gold electrode indicating different feedback modes at differently modified surfaces.     

Synthesis and structural characterization of new phosphinooxazoline complexes of iron

The first phosphinooxazoline chelate complexes of iron were synthesized, and their structural and electronic properties were studied.The known phosphinooxazolines 2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7a), 2-(2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7b), (S)-4-benzyl-2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7e) and (R)-2-(2-(diphenylphosphino)phenyl)-4-phenyl-4,5-dihydrooxazole (7f) were synthesized by a modified three step literature procedure with improved 67-60% overall yields. The new electronically tuned phosphinooxazolines 2-(5-bromo-2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7c), 3-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4-(diphenylphosphino)-N,N-dimethylaniline (7d) and 2-(2-(diphenylphosphino)-3-(trifluoromethyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7g) were synthesized in three to six steps with 59-29% overall yields. Reaction of 7a-f with CpFe(CO)₂I (110 °C, 2 h, toluene) gave the iodide salts of the new iron phosphinooxazoline complexes [CpFe(CO)(7a-f)]⁺ in 87-21% yield. The new complexes were characterized by X-ray and the molecular structures confirm the octahedral coordination geometry and the half-sandwich structure about the iron center. The impact of different oxazoline ligands on the steric and electronic properties of their iron complexes was determined by analysis of selected bond lengths, ν_CO stretching frequency and the oxidation potentials of the ligands and the iron complexes.     

Synthesis,crystal structures and properties of five-coordinate Schiff-base Zn(II) complexes

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N′-bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)) zinc-pyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular π–π stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via π–π stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9?×?6.9?Å) formed through intermolecular π–π stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454?nm, and 480?nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred π–π? transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands.     

Pitting corrosion of zinc in alkaline medium by thiocyanate ions

This paper describes the use of potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques in order to study the pitting corrosion susceptibility of a Zn electrode in KOH solutions containing KSCN as a pitting corrosion agent. Measurements were conducted under different experimental conditions. The results demonstrated that in the absence of KSCN, the anodic voltammetric response displays two anodic peaks prior to reaching the oxygen evolution potential. The first anodic peak A₁ is related to the electroformation of Zn(OH)₂. Peak A₁ is followed by a wide passive region which extends up to the appearance of the second anodic peak A₂. The latter is assigned to the formation of ZnO₂. Addition of SCN⁻ ions to the KOH solutions stimulates the anodic dissolution through peak A₁ and breaks down the passive layer prior to peak A₂. The breakdown potential decreases with an increase in SCN⁻ concentration and temperature, but increases with an increase in KOH concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases slightly with increasing applied positive potential, SCN⁻ concentration, and temperature.     

Studies of interactions among cobalt(III) polypyridyl complexes, 6-mercaptopurine and DNA

The interactions between cobalt polypyridyl coordination compounds Co(L)(3)(3+)(L=1,10-phenanthroline(phen), and bipyridine(bpy)),6-mercaptopurine and calf thymus DNA have been investigated using electrochemical methods(cyclic voltammetry, differential pulse voltammetry), electronic absorption spectroscopy and viscosity measurements. Results indicate that there is an obvious interaction equilibrium between Co(L)(3)(3+), 6-mercaptopurine and DNA. The phenomena are investigated for the first time, and believed to be helpful to use the anticancer drugs more efficiently.     

不同离子液体中硝基苯的电化学还原

研究了硝基苯在N-甲基咪唑对甲基苯磺酸([Mim][PhSO3])和1-丁基-3-甲基咪唑六氟磷酸([Bmim][PF6])两种离子液体中的电化学还原反应.循环伏安法测试显示,硝基苯在[Mim][PhSO3]中只出现一个还原峰,是一个受扩散控制的不可逆电化学反应,而在[Bmim][PF6]中出现两对氧化还原峰,表明其还原产物随离子液体性质的不同而异.     

Reactivity of 17- and 19-electron organometallic complexes. Formation of bent sandwich 19-electron radical cation complexes of ruthenium and osmium

The redox behavior of sandwich indenyl complexes of the general formula (⁵-C₉H₇)ML (M=Ru and L=⁵-C₉H₇ (1), ⁵-C₅H₅ (2), ⁵-C₅Me₅ (3); M=Os, L=⁵-C₉H₇ (4)) has been studied in THF, MeCN, and CH₂Cl₂ by cyclic voltammetry and controlled potential electrolysis on a Pt electrode in the –85 to +20 °C temperature range. The title complexes have been found to undergo reversible one-electron oxidation to the corresponding radical cations, whose stabilities and reactivities depend on the nature of both the metal and °-ligands and of the nucleophilic properties of the solvent. The fast interaction of the electrogenerated 17-electron radical cations with nucleophiles yields bent sandwich 19-electron radical cations, [(⁵-C₉H₇)M(L)(Nu)]⁺ (Nu = Cl^–, MeCN, or THF), the latter undergoing one-electron oxidation to the corresponding [(⁵-C₉H₇)M(L)(Nu)]²⁺ dications. In the case of Nu=THF, the reaction of the electrogenerated 17-electron radical cations with nucleophiles appears to be reversible. Radical cations [(⁵-C₉H₇)₂M]^+· (M=Ru, Os) have been characterized by ESR spectra.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2394–2399, December, 1995.