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

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 TCNQF₂ ¹⁻ and TCNQF₂ ²⁻ materials, identified and proposed as Cu^ITCNQF₂ ^I− and Cu^I ₂(TCNQF₂ ^II−)(CH₃CN)₂, respectively. The existence of two forms of each solid was established by cyclic voltammetry. The low solubility of both Cu^ITCNQF₂ ^I− and Cu^I ₂(TCNQF₂ ^II−)(CH₃CN)₂ solids, facilitated detection of a solid-solid transformation in the presence of [Cu(CH₃CN)₄]⁺. Cu^ITCNQF₂ ^I− 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 Cu^ITCNQF₂ ^I− product obtained by either method was structurally identical. Powder X-ray diffraction studies of Cu^ITCNQF₂ ^I− gave a closely related pattern to that for the thermodynamically stable Cu^ITCNQ^I− phase II (a coordination polymer) rather than the kinetically favoured Cu^ITCNQ^I− phase I. Scanning electron microscopy established the dominant morphology, derived from both electrocrystallized and chemically synthesised samples, were the same. The conductivity of Cu^ITCNQF₂ ^I− as a film on FTO glass was 6.0 × 10⁻⁶ S cm⁻¹, which lies in the semiconducting range.