Volume 6, Issue 2, 1988
8th January, 2023
Influence of the water content in mixed water - acetonitrile solvents upon the kinetics and mechanisms of decomposition and stabilization reactions at the illuminated n - Ga As/TMPD interface.
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by S. Lingier, W.P. Gomes
85-104
DOI: DOI: 10.4152/pea.198802085
The competition between the anodic oxidation of the illuminated n-GaAs electrode and that of tetramethyl-p-phenylenediamine (TKPD) was studied by rotating ring-disk voltammetry as a function of the photo-current density, the TMPD concentration, the pH and the solvent composition, i.e. the water to acetonitrile ratio. From the results, it is concluded that decreasing the water content of the water-acetonitrile mixture influences the kinetics in the sense of improving the stability of the phctoelectrode, and that the subsequent electrochemical decomposition steps may involve either a free hole or a surface intermediate as the mobile surface species, depending on the composition of the electrolyte. These medium effects lead to a better insight into the structure of the decomposition intermediates of GaAs and into their chemical interactions with the solvent.
Polarographic Studies on Mixed Ligand Complexes of Cadmium -1 Methylimidazole - Oxalate System.
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by Gamal B. Mohamed, A. M. Ahmed
105-115
DOI: DOI: 10.4152/pea.198802105
The over-all formation constants of the mixed ligand complexes of 1-methylimidazole (l-Melm) and oxalate (Oxal) with cadmium (II) have been studied polarographically at constant ionic strength, p = 2.0, (NaN03) and pH 8 at 25 + 0.1°C. The reduction of the complexes at a dropping mercury electrode,DME, is reversible and diffusion controlled. The constants for three mixed complexes of Cd(II) are log = 4.0 for Cd(l-Melm)(Oxal), log p12 = 4.4
for Cd(l-Melm) (Oxal)2 and log p2± = 5.9 for Cd(l-Melm)2 (Oxal). The tendency of a ligand to add to a complex and to substitute another ligand was compared.
Novas Complexonas Derivadas de Poliazamacrociclos: Ácido 1, 4, 8, 12 - Tetra-Azaciclopentadecano - N, N', N", N'" – Tetracético.
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by Rita Delgado, J.J.R. Fraústo da Silva
117-133
DOI: DOI: 10.4152/pea.198802117
In the present paper we present the results of a study of the complexes of 1,4,8,12-tetra--azacyclopentadecane-N,N',N';N'''-tetracetic acid (cPENTA) which was synthesized in our laboratory. The stability constants of the complexes of Ca, Sr, Ba, Co, Ni, Cu and Zn and the thermodynamic functions for the formation of the complexes of Ni , Cu and Zn have been determined. The sequence of protonation of the ligand is discussed on the basis of the results of a NMR study and the structure of the complexes of nickel and cobalt is analysed in terms of their respective electronic spectra and of the calculated fractions of the ionic and covalent contributions of the enthalpy changes on formation of these complexes.
Electroreduction of Methyl Isocyanide at Thiomolybdato-Derived Centres: Evidence for an Active Role of Sulphur.
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by Sílvia S.P.R. Almeida, J.J.R. Fraústo da Silva, Rudolf Herrmann et al.
135-140
DOI: DOI: 10.4152/pea.198802135
Reaction of [MoS^][PPh^]^ with methyl isocyanide (CNMe) affords species formulated as [Mo0S,(SCNMe)0][PPh.] or [Mo„S,(CNMe)(CNH)(SCN)][PPh.] in which the isocyanide or the derived ligands undergo cathodic CN bond cleavage to give ammonia, methane and ethylene, in processes involving sulphur as a reductant of the substrate.
