Portugaliae
Electrochimica Acta

The vinylidene complexes trans-[ReCl(=C=CHR)(dppe)2] (R=But, CgH5, C6H4Me-4 or C02Me; dppe = Ph2PCH2CH2PPh2) and the derived carbyne compounds trans-[ReCl(=C-CH2R)(dppe)2]+ undergo, by cyclic voltammetry, in tetrahydrofuran (or acetonitrile), at a Pt electrode, a single-electron reversible oxidation. The electrochemical PL ligand parameter has been estimated for these ligands.

The nitrile complexes trans-[ReCl(NCR)(dppe)21 (l;R=alkyl or aryl, dppe = Ph2PCH2CH2PPh2) undergo, in tetrahydrofuran, by cyclic voltammetry and at a Pt electrode, two successive single¬-electron reversible (or quasi-reversible) oxidations and, from the values of the half-wave oxidation potential (E i/2) of the first anodic wave, the electrochemical PL ligand parameter was estimated for the nitrile ligands indicating that they behave as better net electron donors than isocyanides, dinitrogen or carbonyl ligands. For the aromatic nitrile complexes, E i/2 is shown to vary linearly with the Hammett's Op constant of the phenyl substituent.

The electrochemical behaviour of mer-[ReCl(N2)L {P(OMe)3}3] (1,L = CNR or PPh3), trans-[ReCl(N2) {P(OMe)2Ph>4] (2), [ReCl(N2)(CNMe)(PPh3){P(OEt)3}2] (3) and [ReCl(N2)(CNMe)2(PBu2Ph)2] (4) was studied by cyclic voltammetry and controlled potential electrolysis, in tetrahydrofuran (or NCMe), at a Pt electrode. They undergo a one-electron quasi-reversible oxidation and, by comparing the values of E 1/2 (also with others reported in the literature), the following order of he n - acceptor/o-donor ability was established: CO > CNMe, CNEt, CNBufc > P(OMe)3 >" P(OMe)2Ph > PPh3, Ph2PCH2CH2PPh2 > PMe2Ph.

The redox potential of a variety of ferrocene derivatives has been measured by cyclic voltammetry and correlated linearly with the Hammett's Op or the Taft polar a constant of the substituent; the latter correlation has been recognized for the 3 sp -C ligating substituents.

The corrosion behaviour of hot dip ( Zn and Al) steel parts heated at diferent temperatures and for varying periods of times has been investigated. Mathematic-statistical treatment of results obtained has been applied. This work show the better protection of steel at high temperature with the aluminized in front of galvanized.

The evolution oi the polarization anodic curves of amorphous, Metglass 2826 alloys in S042~ , PCn3- dilute solutions, has been studied electrcchemically. These results show the ranges where they are active (fast metal dissolution) and or passive (formation of protective layers). The mechanisms and interaction parameters through the electrolyte/metal interface have been studied too.