MANGANESE(II) AND (III) COMPLEXES WITH 4-METHOXY-2-QUINOLINECARBOXYLIC ACID - MONONUCLEAR AND BINUCLEAR IN APROTIC MEDIUM

The redox chemistry of the ligand 4-methoxy-2-quinolinecarboxylic acid, its monoanion and its complexes with manganese(II) and manganese(III) has been studied in dimethylsulphoxide using electrochemical, spectroscopic and magnetic measurements. The combination of the monoanion of the ligand with manganese(II) in a 1:2 mole ratio forms a pale yellow mononuclear complex whose stability constant has been determined spectrophotometrically and is 5 x 10(9) M-2 (25-degrees-C). Its oxidation at +0.76 V vs SCE yields a brown complex of manganese(III) which is binuclear. This complex is reduced at +0.67 V vs SCE generating a green Mn(II)-Mn(III) mixed-valence complex, and a second reduction at -0.16 V vs SCE regenerates the mononuclear manganese(II) complex. These results may be useful to the development of effective catalysts for the electrochemical oxidation of organic molecules.