Controlled potential electrodeposition of a microcrystalline thin film of the charge transfer material tetrathiafulvalene–polyoxometalate of approximate composition (TTF)5.3(Bu4N)0.7[P2W18O62]·3H2O

Abstract

Electrocrystallisation provides a systematic approach to the preparation of tetrathiafulvalene (TTF)–polyoxometalate materials in the form of films having significant conductivity. In this study, a highly uniform microcrystalline thin film derived from TTF⁺ and the Dawson–Wells anion [α-P₂W₁₈O₆₂]⁶⁻ has been deposited onto glassy carbon, gold and indium tin oxide surfaces by controlled potential oxidative electrolysis of TTF in the presence of K₆[P₂W₁₈O₆₂] in acetonitrile (0.1 M [Bu₄N][PF₆]). Elemental analytical data are consistent with the formation of this conducting charge transfer salt having the approximate composition (TTF)_5.3(Bu₄N)_0.7[P₂W₁₈O₆₂]·3H₂O. Spectroscopic data support this conclusion. Mechanistic aspects of the electrocrystallisation process have been monitored by cyclic voltammetry, electrochemical quartz crystal microbalance and chronoamperometric methods. A less crystalline form of this material with a slightly different composition also can be produced by bulk electrolysis of TTF to TTF⁺ followed by addition of K₆[P₂W₁₈O₆₂]. The conductivity of the film at room temperature is in the semiconducting range. The EPR spectra, together with the field strength and temperature dependence of the magnetic susceptibility, suggest that regions of film behave as a quasi one-dimensional system, with antiferromagnetic and spin-flop behaviour at low temperatures. The Raman spectra are consistent with an average TTF charge state of +1, while voltammetry confirms the presence of [P₂W₁₈O₆₂]⁶⁻. The morphology and crystallinity of the electrocrystallised and chemically prepared materials were investigated by scanning electron microscopy and X-ray diffraction, respectively.