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Redox and Acid–Base Chemistry of 7,7,8,8-Tetracyanoquinodimethane, 7,7,8,8-Tetracyanoquinodimethane Radical Anion, 7,7,8,8-Tetracyanoquinodimethane Dianion, and Dihydro-7,7,8,8-Tetracyanoquinodimethane in Acetonitrile

Le, Thanh Hai, Nafady, Ayman, Qu, Xiaohu, Bond, Alan M., Martin, Lisandra L.
Analytical chemistry 2012 v.84 no.5 pp. 2343-2350
acetonitrile, anions, electrochemistry, silver, tetrahydrofuran
The chemistry and electrochemistry of TCNQ (7,7,8,8-tetracyanoquinodimethane), TCNQ•–, TCNQ²–, and H₂TCNQ in acetonitrile (0.1 M Bu₄NPF₆) solution containing trifluoroacetic acid (TFA) has been studied by transient and steady-state voltammetric methods with the interrelationship between the redox and the acid–base chemistry being supported by simulations of the cyclic voltammograms. In the absence of acid, TCNQ and its anions undergo two electrochemically and chemically reversible one-electron processes. However, in the presence of TFA, the voltammetry is considerably more complex. The TCNQ²– dianion is protonated to form HTCNQ–, which is oxidized to HTCNQ•, and H₂TCNQ which is electroinactive over the potential range of −1.0 to +1.0 V versus Ag/Ag⁺. The monoreduced TCNQ•– radical anion is weakly protonated to give HTCNQ•, which disproportionates to TCNQ and H₂TCNQ. In acetonitrile, H₂TCNQ deprotonates slowly, whereas in N,N-dimethylformamide or tetrahydrofuran, rapid deprotonation occurs to yield HTCNQ– as the major species. H₂TCNQ is fully deprotonated to the TCNQ²– dianion in the presence of an excess concentration of the weak base, CH₃COOLi. Differences in the redox and acid–base chemistry relative to the fluorinated derivative TCNQF₄ are discussed in terms of structural and electronic factors.