Tetrathiafulvalene-based double metal lead iodides: structures and electrical properties

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 MCl₆^3- 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 MCl₆^3- occurred sequentially. In isostructural TTF₃InCl₆ and TTF₃SbCl₆, the intermolecular interaction between MCl₆^3- 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, 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 MCl₆^3- 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.