Synthesis, physical properties, structural, and electrochemical characterization of methimidazolium and imidazolium-based tetracyanoquinodimethane anion radical salts

Two methimazolium and two imidazolium-based salts derived from combination with the tetracyanoquinodimethane (TCNQ) radical anion have been synthesized (1-4). The 1: 1 (cation: anion) stoichiometry of the chemically synthesized materials is fully supported by steady-state voltammetric measurements at a microdisc electrode in acetonitrile. The methimazolium TCNQ salts (1 and 2), which contain an acidic proton on the cation, exhibit a protonation step coupled to the TCNQ(1-/2-) charge-transfer process. Solid-solid transformations at a TCNQ-modified electrode also lead to electrochemical synthesis of 1-4, but also indicate that other cation: anion stoichiometries are accessible. Atomic force microscopy for electrochemically synthesized samples exhibit rod-like morphology. Conductivity measurements on chemically and electrochemically prepared salts are in the semiconducting range. Scanning electrochemical microscopy approach curve data support the substantial conductivity of these solids. Extensive physicochemical characterization of these materials is in complete accordance with the X-ray crystal structure of 1-acetonitrile-3-methylimidazolium tetracyanoquinodimethane, [AMim(+)][TCNQ(1-)], 4.