Electrode reactions of 8-mercaptoquinoline and manganese(II)-8-mercaptoquinolinato complexes in non-aqueous solvent

Abstract The electrode reactions of 8-mercaptoquinoline and manganese (II)-8-mercaptoquinolinato complexes at a dropping mercury electrode (DME) and a glassy, carbon electrode (GCE) have been studied in N,N-dimethylformamide (DMF). The sodium salt of 8-mercaptoquinoline (8-MQNa) undergoes a reversible one-electron oxidation wave (E1/2=−0.878 V vs. SCE) and an irreversible two-electron reduction wave (E1/2=−2.188 V vs. SCE) at the DME. The existence of bis- and tris-complexes of manganese (II), i.e. [Mn(8-MQ)2] and [Mn(8-MQ)3]−, has been established by analysing the polarograms and absorption spectra. These redox processes have been examined by polarography, cyclic voltammetry, controlled potential electrolysis, and spectrophotometry. These complexes undergo a one-electron oxidation wave at the GCE and a two-electron reduction wave at the DME. Manganese (II) compounds show complex behaviour for the oxidation waves at the DME. The proposed oxidation mechanisms at the DME are: [Mn(8-MQ)2]+Hg→Mn2++[Hg(8-MQ)2]+2 e− or 2[Mn(8-MQ)3]−+Hg ag2[Mn(8-MQ)2]+[Hg(8-MQ)2]+2 e− [Mn(8-MQ)2]+Hg→Mn2++[Hg(8-MQ)2]+2 e− and the reduction steps can be expressed by the following schemes: [Mn(8-MQ)2]+2 e−→[Mn(8-MQ)2]2− or [Mn(8-MQ)3]−+2 e−→[Mn(8-MQ)2]2−+(8-MQ)− (8-MQ)−+2 e−→(8-MQ)3− [Mn(8-MQ)3]− undergoes a single one electron oxidation step at the GCE: [Mn(8-MQ)3]− ag[Mn(8-MQ)3]+e− The oxidation mechanism of [Mn(8-MQ)2] at the GCE is also proposed.