PHYSICOCHEMICAL CHARACTERIZATION OF THE 1,2-BIS(CYANIMIDO)CYCLOBUTENE-3,4-DIONE DIANION AND ITS TWIN RADICAL-ANIONS

Controlled oxidation of the 1,2-bis(cyanoimido)cyclobutene-3,4-dione ( CMCB) dianion in aprotic solvents gives electron paramagnetic resonanc e (EPR) spectra characteristic of the presence of two radical species in a fixed mole ratio, identified as two planar conformers of the mono anion of CMCB differing in the orientation of one of the two N-C equiv alent to N groups. Consideration of the nature and symmetry of the mol ecular orbitals, and of the IR and C-13 NMR spectra, suggests that sim ilar isomers should also be present in the solution of the dianion. Cy clic voltammograms of the dianion in N,N-dimethylformamide exhibit two oxidation peaks, the first being due to a one-electron diffusion-cont rolled reversible process, and the second to an irreversible process. Computer simulation of the cyclic voltammetric curves for the first pr ocess indicates that the observed behaviour is consistent with the fou r-member square scheme suggested by EPR, IR and NMR experiments. The i rreversibility of the second peak is due to the presence of fast chemi cal reactions involving the product of one-electron reversible oxidati on of the radical anion.