Dicyanomethylene derivatives of squaric acid: Electrochemical behaviour and ESR investigation

The electrochemical behaviour of mono- and bisdicyanomethylene-substituted squaric acid dianion was investigated in dimethylformamide and acetonitrile on a Pt electrode. In cyclic voltammetry the oxidation of these dianions involves two successive, chemically reversible, one-electron processes, affording the corresponding radical anions and neutral species. The redox potentials are strongly dependent upon the number of dicyanomethylene substituents. Whereas the neutral species are stable only in the time scale of the voltammetric experiments, the radical anions can be accumulated by macroscale electrolysis. The ESR spectra of these radicals are reported. The monosubstituted dianion is protonated by electrochemical oxidation of hydrogen, whereas the disubstituted ones are not. Compounds obtained from the disubstituted dianions and the methyl viologen dication are also described.