The title compound (1) is reduced in a stepwise two-electron process to its dianion. It has been confirmed that potential inversion occurs both in acetonitrile and acetonitrile+water (83%/17%, v/v). By this it is meant that insertion of the first electron is actually more difficult than insertion of the second, i.e. Edegrees(1)-Edegrees(2) is negative (where Edegrees(1) and Edegrees(2) are the standard potentials for the two reduction steps). The value of Edegrees(1)-Edegrees(2) in the acetonitrile+water mixed solvent is -0.08+/-0.01 V which corresponds to about 8 U mol(-1). Other aspects of the electrochemical reduction of 1 are discussed, including the fact that the dianion is unstable on the voltammetric timescale in pure acetonitrile but is stabilized by the presence of water. The electron-transfer kinetics are more sluggish on solid electrodes (platinum or glassy carbon) than on mercury, which was used for the determination of Edegrees(1)-Edegrees(2). Theoretical calculations (DFT and AM1) have been carried out to indicate the structural changes that accompany the reduction of 1 to its radical anion and dianion, and the role of these structural changes in the development of potential inversion is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.