Electrochemistry of TCNQF2 in acetonitrile in the presence of [Cu(CH3CN)4]+: Electrocrystallisation and characterisation of CuTCNQF2

Abstract

The bulk electrochemical reduction of TCNQF2 (where TCNQF2 = 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile (0.1 M Bu4NPF6) in the presence of [Cu(CH3CN)4]+ leads to the electrocrystallisation of TCNQF21− and TCNQF22− materials, identified and proposed as CuITCNQF2I− and CuI2(TCNQF2II−)(CH3CN)2, respectively. The existence of two forms of each solid was established by cyclic voltammetry. The low solubility of both CuITCNQF2I− and CuI2(TCNQF2II−)(CH3CN)2 solids, facilitated detection of a solid-solid transformation in the presence of [Cu(CH3CN)4]+. CuITCNQF2I− was synthesized chemically as a dark blue microcrystalline solid by reaction of TCNQF2 and CuI in CH3CN, as well as electrochemically. Electronic and vibrational spectroscopic methods confirmed the CuITCNQF2I− product obtained by either method was structurally identical. Powder X-ray diffraction studies of CuITCNQF2I− gave a closely related pattern to that for the thermodynamically stable CuITCNQI− phase II (a coordination polymer) rather than the kinetically favoured CuITCNQI− phase I. Scanning electron microscopy established the dominant morphology, derived from both electrocrystallized and chemically synthesised samples, were the same. The conductivity of CuITCNQF2I− as a film on FTO glass was 6.0 × 10−6 S cm−1, which lies in the semiconducting range.