Portugaliae
Electrochimica Acta

The electrochemical data obtained by cyclic voltammetry on several camphor-type (A, B and C) ligands and derived complexes are revised. A direct positive correlation is established between the redox potentials (anodic or cathodic) of the camphor species and the σp-Hammett parameter of the R group on the camphor skeleton. A study of the effect of the ligand on the redox properties of some Pd, Pt or Cu camphor complexes shows that the ligands influence either the anodic or cathodic processes but the characteristics of the metal drive the potential values.

This work reports on cyclic voltammetry and spectroscopic UV-Vis investigations of some pyridazine derivatives 1-8 in dimethylformamide. In the electrochemical study, monochlorinated pyridazines 2-8 exhibit two reductions but in the case of dichlorinated derivative 1 an additional wave is seen for the reduction of the second carbon-chloride bond. The electronic absorption spectra display an intramolecular charge transfer band π-π* in the UV region of which depend substantially on the nature of both donor and acceptor moieties. These results indicate the π-electron delocalization in the conjugated system.

The bis(cyanoimide) complex trans-[Mo(NCN)2(dppe)2] (dppe = Ph2PCH2CH2PPh2) is susceptible of electrophilic attack to form the acylated and aroylated derivatives trans-[MO(NCN){NCNC(O)R}(dppe)2]Cl (R = Et 2a or Ph 2b). Herein, we report a preliminary study on the electrochemical behaviour of complexes 2 and the derivative trans-[Mo(NCN)Cl(dppe)2][BF4] 3, as investigated by cyclic voltammetry (CV) and controlled-potential electrolysis (CPE), what has allowed a comparison of the electron-donor ability of the ligands.

The electrochemical properties of a series of &[M(R,R’timdt)2&] dithiolenes (M = Ni, Pd, Pt; R,R’timdt = monoanion of disubstituted imidazolidine-2,4,5-trithione) have been studied by cyclic voltammetry, controlled potential coulometry, and EPR spectroscopy. All the compounds undergo two separate one-electron reductions and one two-electron oxidation, which proceed through a single step in the case of nickel complexes, and through two separate steps in the case of palladium and platinum complexes. Inductive effects played by the R and R’ substituents influence the formal electrode potentials of the electron transfer processes. EPR spectroscopy has proved that the unpaired electron in monoanions [M(R,R’timdt)2]- is located on a SOMO, which, even if mainly ligand centred, is significantly contributed by the metal.

The complexation of nitriloacetic acid (NTA) with copper and lead was studied by square wave stripping voltammetry (SWSV) using a mercury iridium microelectrode as the working electrode. The results show that NTA interfere with the measurements, but if the mercury iridium microelectrode is coated with different concentrations of agarose (0.75%, 1.5% and 15% w/v) this interference is greatly minimized. The best results were obtained with 1.5% agarose.

A flux cell with vitreous carbon tubular electrodes, as auxiliary and working electrodes, was tested. The following procedure was used: (1) study and optimization of the mercury deposition conditions at the working electrode, (2) study the electrodes position and distance in order to minimize dispersion of the sample, (3) study of the linearity and reproducibility using different concentrations of manganese (2.10-7 to 6.10-7 M), with differential pulse anodic stripping voltammetry (DPASV) and square wave stripping voltammetry (SWSV). Good linear correlation was obtained for concentration of manganese used.