Browsing by Author "Bodini, ME"

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    Manganese-quinizarin-pyrazinecarboxylic acid mixed-ligand complex in aprotic media. Formation of a manganese(III)-semiquinone binuclear species
    (KLUWER ACADEMIC PUBL, 1999) Bodini, ME; del Valle, MA; Copia, G; Jara, F
    The monoanion of pyrazincarboxylic acid (PcA(-)), the dianion of quinizarine (Qz(=)) and manganese(II) yield a soluble deep-blue complex in dimethylsulphoxide whose Mn-II:Qz(=):PcA(-) stoichiometry has been established as 1:1:1. This mixed-ligand complex is oxidized in two steps, each involving one equivalent of charge per complex present, as indicated by controlled-potential electrolyses done at +0.30 V versus s.c.e. and +0.50 V versus s.c.e.. The association between the metal ion and the ligands prevail and the oxidations finally produce a dark-red complex which possesses the same stoichiometry as the original deep-blue species. In the latter the metal ion is present in oxidation state +3 with the quinizarine dianion as the corresponding semiquinone of the oxidized quinizarine. The monoanion of pyrazincarboxylic acid remains unchanged. Controlled-potential electrolysis at -0.20 V versus s.c.e. of a solution of the mixed-ligand complex indicates that it is binuclear, generating a Mn-II-Mn-III mixed-valence species. The latter is, in turn, reduced at -1.60 V versus s.c.e. producing probably a mononuclear of manganese(II) species. If manganese(II) is combined with the semiquinone of quinizarine the metal ion exhibits the magnetic characteristic of manganese(III) and the semiquinone is reduced to the quinizarine dianion, indicating that the mixed-ligand formed exhibits intramolecular charge-transfer. This is a good example of a binuclear species accumulating four oxidation equivalents after oxidation of both metal centers and the quinizarine ligands.
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    Voltammetric and spectroscopic study of the manganese-quinizarine-quinaldic acid mixed-ligand complex in dimethylsulfoxide
    (PERGAMON-ELSEVIER SCIENCE LTD, 1997) Bodini, ME; delValle, MA; Caceres, S
    The combination of manganese(II) with quinizarine and the monoanion of quinaldic acid in dimethylsulfoxide yields a soluble deep-blue complex whose Mn-II:Qz(2-):ACQ(-) stoichiometry is 1:1:2. This complex is oxidized in two steps each involving one equivalent of charge per metal ion as indicated by controlled-potential electrolyses at +0.30 V vs S.C.E. and +0.45 V vs S.C.E. The association between the metal ion and the ligands prevails and the oxidations produce finally a dark-red complex of the same stoichiometry as the original deep-blue species. In the latter the metal is in the oxidation state +3 and the quinizarine dianion has been oxidized to the semiquinone form. The monoanion of quinaldic acid is unchanged.
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    Voltammetric study of the redox chemistry of 2,3-dihydroxy-quinoxaline and its zinc complexes in non-aqueous medium
    (PERGAMON-ELSEVIER SCIENCE LTD, 1998) Bodini, ME; del Valle, MA; Copia, GE; Soto, C
    The electrochemical behaviours of 2,3-dihydroxy-quinoxaline (2,3-DH(2)Qx) and the complex species formed with zinc(II) have been studied in non-aqueous media. Using dimethylsulphoxide or N,N-dimethylformamide as solvents the monoanion of the ligand is obtained quantitatively after reduction of one of the hydroxylic protons. The reduction potential for the hydroxylic proton is -1.93 V vs S.C.E. in DMSO and -1.68 V vs S.C.E. in DMF, reflecting the different donor number of the solvents. If acetonitrile is used, the simultaneous reduction of both hydroxylic protons is observed. The oxidation to the semiquinone is observed at -0.12 V us S.C.E. in DMSO and DMF whereas it appears at -0.02 V us S.C.E. in acetonitrile.