A Platform to Evaluate the Effect of Back Charge Transfer on the Electrical Conductivity of TTF Charge Transfer Complexes: TTF 3 MCl 6 (M = In, Sb).

TTF 3 MCl 6 (M = In, Sb) series were developed for an ideal platform to investigate the effect of back charge transfer of MCl 6 3- 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 MCl 6 3- occurred sequentially. In isostructural TTF 3 InCl 6 and TTF 3 SbCl 6 , the intermolecular interaction between MCl 6 3- 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, TTF 3 InCl 6 shows 3-orders of magnitude higher electrical conductivity compared to TTF 3 SbCl 6 . 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 MCl 6 3- in TTF 3 InCl 6 compared to TTF 3 SbCl 6 , which is due to the lower electronegativity of In, considering that the only difference between the two compounds is the center metal.