Gregory Ginzburg

The electrochemical oxidation of divalent nickel complexes with tetra-aza-macrocyclic ligands in aqueous solutions

Abstract The electrochemical oxidation of three divalent nickel complexes with tetra-aza-macrocyclic ligands in perchlorate- and sulphate-containing aqueous solutions is reported. The mechanism of oxidation is analysed in detail. Redox potentials, diffusion coefficients, a transfer coefficient and a heterogeneous rate constant are reported. The pH effect on the electrochemical oxidations is discussed.

“Inverted” peaks and current oscillations in cyclic voltammetry

Abstract Inverted peaks and strongly increased peaks have been reported and different explanations of these phenomena have been suggested[1,2]. The present communication discusses the peak shape distortions (“inverted” peaks, current oscillations) in terms of tangential movements of the mercury electrode surface. These distortions are explained similarly to the maxima in classical polarography: inhomogeneous polarization and inhomogeneous adsorption are considered as the two major forces causing the mercury surface movement and as a result, leading to the peak shape distortions. Experimental examples of the phenomena in aprotic and protic media and for organic and inorganic redox couples are given and explained in accordance with the proposed theory.

A polarographic study of Cd(II)-NTA complexes in alkaline solution

Up to four d.c. polarographic waves were observed on voltammetric curves of Cd(II)-nitrilotriacetate complexes on the DME in the pH range 7.0–11.5. These polarograms are analyzed using a non-linear least squares method and the mechanism of the electrode reactions and prior homogeneous reaction are discussed. The kinetic parameters of the separate reactions are calculated and compared with literature values. The accelerating influence of OH− ions on the dissociation of the complexes is established.

Redox properties of a Cu(II) complex with a macrocyclic diene N4 ligand

Abstract The mechanism of the electrochemical reduction of the Cu(II) complex with trans -Me 6 -cyclotetra-aza(14)diene in aqueous solutions was studied in detail. The electrochemical oxidation of the same complex was also analysed, as well as its role as an electrocatalyst for the oxidation of water.

A mechanistic study on the anodic oxidation of 1,1-dimethylallene (DMA): A semi-empirical method for resolving irreversible overlapping waves in cyclic voltammetry

Abstract The anodic oxidation of the titled compound has been studied in acetonitrile at a platinum anode in the presence of tetraethylammoniumfluoborate and lithium perchlorate as supporting electrolytes. In the presence of the former electrolyte the cylcic voltammogram exhibits two moderately separated waves, whereas in the presence of the latter the waves overlap each other completely. An ECE mechanism is proposed in either electrolyte. The two moderately overlapping waves obtained for the oxidation of DMA in the presence of BF 4 − have been resolved into two separate waves with equal heights, by employing a semi-empirical method. Studies of the effect of electrolyte concentration on the shift in anodic peak potentials are presented and discussed in terms of specific and non-specific adsorption of ClO 4 − and BF 4 − .

The influence of disproportionation of the anion radical on the electrochemical reduction of 1,9-dimethyldibenzo[b,f]pentalene

Abstract The electrochemical reduction of 1,9-dimethyldibenzo[b,f]pentalene has been investigated in DMF by both cyclic voltammetry (CV) and dc polarography. The influence of the depolarizer concentration and electrode material (Pt and Hg) was studied. It was found that the first electron transfer is a reversible one under most conditions studied, whereas the second electron transfer was irreversible on Pt and quasi-reversible on the HMD. An overall EDISP.EC mechanism was suggested and discussed. It turned out that the first reduction process was accompanied by a disproportionation of the anion-radical to its parent hydrocarbon and dianion. The experimental waves were analysed on the basis of various theoretical procedures.

Electrochemical preparation of stable nickel(III) complexes with tetradentate macrocyclic ligands in aqueous solutions

Stable solution of NiIII complexes of the 14-membered macrocylic ligands (I), (II), and (III) were obtained by electrochemical oxidation on gold and platinum electrodes of the corresponding NiII complexes in mild acidic aqueous solutions in the presence of sulphate; the NiIII complexes formed represent a new kind of strong, easily accessible, single-electron, oxidizing agent with E°ca. 1 V vs. standard hydrogen electrode (S.H.E.) in aqueous media.

Comparative study of the electrochemical and pulse-radiolytic oxidation of the complexes of nickel(II) and copper(II) containing 1,4,8,11-tetra-azacyclotetradecane

Electrochemical and pulse-radiolytic oxidation of [Ni(cyclam)]2+ and [Cu(cyclam)]2+(cyclam = 1,4,8,11-tetra-azacyclotetradecane) have been studied in aqueous acidic perchlorate and sulphate media. As with other nickel macrocyclic systems, [Ni(cyclam)]2+ is oxidized to NiIII, the stability of which is enhanced by sulphate complexation. In contrast, [Cu(cyclam)]3+ is much less stable than the nickel analogue and does not form a stable sulphate complex. Electrochemical oxidation of [Cu(cyclam)]2+ at pH 1.6 is a multistep process which is catalysed by sulphate ion. The mechanism appears to involve the transfer of four electrons resulting in a copper(II) macrocyclic diene complex.

Stabilization of monovalent nickel in aqueous solutions by a saturated tetra-aza-macrocyclic ligand

The planar form of the complex C-meso-1,4,5,7,7,8,11,12,14,14-decamethyl-1,4,8,11-tetra-azacyclotetradecanenickel(I){[Ni(L1)]+}is shown to be stable in aqueous solutions, with t½ > 100 h and the formal potential of the couple [Ni(L1)]2+/[Ni(L1)]+ is – 0.98 V vs. standard calomel electrode; redox reactions involving this couple were studied and compared with those of the couple [Ni(L2)]2+/[Ni(L2)]+(L2=C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane).

Electrocatalytic oxidations on chemically modified electrodes prepared by anodic deposition of a nickel complex with a tetra-azamacrocyclic ligand

A precipitate is formed on anodes in alkaline solutions containing 1,4,8,11-tetra-azacyclotetradecane-5-7-dionatonickel(II); this precipitate acts as an electrocatalyst for the oxidation of water alcohols, and chloride.