Synthesis and Properties of a Mixed-Valence Compound with Single-Step Tunneling and Multiple-Step Hopping Behavior
Résumé
The org. precursor bis(trimethylsilylethynyl)TTFMe2 (3, TTF = tetrathiafulvalene) was prepd. as a 1:1 mixt. of the cis and trans isomers. Pure samples of 3-cis and 3-trans were obtained by crystn. and identified by XRD anal. The treatment of pure 3-trans and a 1:1 mixt. of 3-cis/trans with (i) potassium carbonate, (ii) the iron complex Cp*(dppe)FeCl [5, Cp* = η5-C5Me5, dppe = 1,2-bis(diphenylphosphanyl)ethane] in the presence of KPF6, and (iii) tBuOK provided Cp*(dppe)Fe-C C-TTFMe2-C C-Fe(dppe)Cp* as the pure geometric isomer 6-trans (85 %) and as the 60:40 mixt. 6-cis/trans (63 %), resp. The oxidn. of 6-trans with [(C5H5)2Fe]PF6 gave [6-trans][PF6]n (n = 1-3). Visible, IR, near-IR (NIR), and ESR (EPR) spectroscopy together with DFT data show that [6-trans][PF6] is a class II mixed-valence complex (Hab = 85 cm-1) in which the spin distribution depends on the conformation of the mol. Intramol. electron transfer occurs through single-step tunneling and a multistep hoping mechanism. The triplet state is thermally accessible for [6-trans][PF6]2.