MECHANISTIC ASPECTS OF THE ELECTROCHEMICAL REDUCTION OF 7,7,8,8-TETRACYANOQUINODIMETHANE IN THE PRESENCE OF MG2+ OR BA2+

The effect of aggregation of Mg2+ or Ba2+ (M2+) and electrochemically generated reduced forms of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in acetonitrile solution was studied by voltammetric and chronoamperometr ic techniques, the electrochemical quartz crystal microbalance (EQCM), ESR spectroscopy, and atomic force microscopy (AFM). Although the mon oreduced form, TCNQ(.-), appears not to interact strongly with either metal cation on the voltammetric time scale, the dianion TCNQ(2-) was found to interact and to form a thin layer deposit of the type M(TCNQ) . The potential at which this occurs was less negative than the potent ial required for the formation of the free dianion in solution, reflec ting the binding with the metal cation. Unusually, the initial deposit ion of M(TCNQ) triggered the deposition of a material possibly M(TCNQ) (2) as evidenced by, first, a characteristic voltammetric response, se cond, a strong ESR signal, and third, the gravimetrically determined d eposited mass per charge passed. Both types of deposit gave distinct v oltammetric signatures, and an overall scheme for the process is propo sed.