Raman spectroscopic study of the adsorption states of the N, N'-dimethyl 4, 4'-bipyridinium ion and of its monoradical cation at a silver electrode

A study of the adsorption states of the N, N'-dimethyl-4, 4'-bipyridinium (MV++) cation at a silver electrode in aqueous KX (X = Cl or I) solutions has been undertaken through Raman spectrometry. On an oxidized silver electrode, the MV++ cation is adsorbed as a complex MVX2, 2AgX. After reduction of the AgX layer, MV++ remains adsorbed and probably forms a (Ag°)nMV++ complex. At a potential of — 0,600 V/SCE the MV+.monoradical forms and is probably stabilized through complexation in the silver colloidal layer. In the two latter cases the Raman spectra shows a strong intensity enhancement. An assignment of the vibrational spectra of the MV++ cation is proposed through comparison with that of biphenyl and N-methylpyridinium chloride.