VOLTAMMETRIC AND SPECTROSCOPIC STUDIES OF THE BEHAVIOR OF MANGANESE(II) AND MANGANESE(III) COMPLEXES WITH ISOQUINOLINECARBOXYLIC ACID IN APROTIC MEDIUM

The redox chemistry of the manganese(II) and manganese(III) complexes with 1-isoquinolinecarboxylate (1-IQC) in dimethylsulphoxide has been studied. Cyclic voltammetry, polarography, controlled-potential electrolysis, UV-vis spectroscopy and magnetic susceptibility measurements have been performed on the solutions. In the presence of the anion 1-isoquinolinecarboxylate the manganese(II) ion forms an Mn(II)(1-IQC)2 complex, whose conditional formation constant has been evaluated polarographically and turns out to be 5 x 10(7) M-2 at 25-degrees-C. The polarograms of the solution of this complex show a cathodic wave with E1/2 = -1.60 V vs S.C.E., corresponding to the reduction of the metal ion with its subsequent destruction. On the other hand the voltammograms on a platinum electrode show the reduction of the bound ligand at -1.66 V vs S.C.E., probably to a bound radical species, and two oxidation processes at -1.37 and -1.49 V vs S.C.E. The manganese(II) complex does not decompose after this reduction, but the species produced was not obtained quantitatively as the reduction potential was too close to the solvent discharge. The manganese(II) complex is oxidized to the Mn(III)(1-IQC)3 mononuclear complex, whose conditional formation constant was evaluated polarographically and turns out to be 4 x 10(14) M-3 at 25-degrees-C.