A Platform to Evaluate the Effect of Back Charge Transfer on the Electrical Conductivity of TTF Charge Transfer Complexes: TTF3MCl6 (M = In, Sb)

TTF3MCl6 (M = In, Sb) series were developed for an ideal platform to investigate the effect of back charge transfer of MCl63- on electrical conductivity depending on the metal ions. They were successfully synthesized by a UV light-induced one-pot reaction where TTF oxidation and formation of MCl63- occurred sequentially. In isostructural TTF3InCl6 and TTF3SbCl6, the intermolecular interaction between MCl63- and TTF induces back charge transfer, which were confirmed by the crystal structure and spectroscopic analysis. Despite the similar crystal structure in terms of intermolecular distance, TTF3InCl6 shows 3-orders of magnitude higher electrical conductivity compared to TTF3SbCl6. According to the cyclic voltammograms (CV) and electron spin resonance (ESR) spectra, increased conductivity is because of the higher degree of back charge transfer from MCl63- in TTF3InCl6 compared to TTF3SbCl6, which is due to the lower electronegativity of In, considering that the only difference between the two compounds is the center metal.