Physicochemical characterization of the 1,2-bis(cyanimido)cyclobutene-3,4-dione dianion and its twin radical anions

Abstract

Controlled oxidation of the 1,2-bis(cyanoimido)cyclobutene-3,4-dione (CMCB) dianion in aprotic solvents gives electron paramagnetic resonance (EPR) spectra characteristic of the presence of two radical species in a fixed mole ratio, identified as two planar conformers of the monoanion of CMCB differing in the orientation of one of the two N—CN groups. Consideration of the nature and symmetry of the molecular orbitals, and of the IR and ¹³C NMR spectra, suggests that similar isomers should also be present in the solution of the dianion.

Cyclic voltammograms of the dianion in N,N-dimethylformamide exhibit two oxidation peaks, the first being due to a one-electron diffusion-controlled reversible process, and the second to an irreversible process. Computer simulation of the cyclic voltammetric curves for the first process indicates that the observed behaviour is consistent with the four-member square scheme suggested by EPR, IR and NMR experiments. The irreversibility of the second peak is due to the presence of fast chemical reactions involving the product of one-electron reversible oxidation of the radical anion.