Synthesis and Properties of a Mixed‐Valence Compound with Single‐Step Tunneling and Multiple‐Step Hopping Behavior

The organic precursor bis(trimethylsilylethynyl)TTFMe 2 ( 3 , TTF = tetrathiafulvalene) was prepared as a 1:1 mixture of the cis and trans isomers. Pure samples of 3 ‐ cis and 3 ‐ trans were obtained by crystallization and identified by XRD analysis. The treatment of pure 3 ‐ trans and a 1:1 mixture of 3 ‐ cis / trans with (i) potassium carbonate, (ii) the iron complex Cp*(dppe)FeCl [ 5 , Cp* = η 5 ‐C 5 Me 5 , dppe = 1,2‐bis(diphenylphosphanyl)ethane] in the presence of KPF 6 , and (iii) t BuOK provided Cp*(dppe)Fe–C≡C–TTFMe 2 –C≡C–Fe(dppe)Cp* as the pure geometric isomer 6 ‐ trans (85 %) and as the 60:40 mixture 6 ‐ cis / trans (63 %), respectively. The oxidation of 6 ‐ trans with [(C 5 H 5 ) 2 Fe]PF 6 gave [ 6 ‐ trans ][PF 6 ] n ( n = 1–3). Visible, IR, near‐IR (NIR), and electron paramagnetic resonance (EPR) spectroscopy together with DFT data show that [ 6 ‐ trans ][PF 6 ] is a class II mixed‐valence complex ( H ab = 85 cm –1 ) in which the spin distribution depends on the conformation of the molecule. Intramolecular electron transfer occurs through single‐step tunneling and a multistep hoping mechanism. The triplet state is thermally accessible for [ 6 ‐ trans ][PF 6 ] 2 .