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

• Published in: European journal of inorganic chemistry Vol. 2014; no. 24; pp. 3899 - 3911
• Main Authors: Makhoul, Rim, Kumamoto, Yuki, Miyazaki, Akira, Justaud, Frédéric, Gendron, Frédéric, Halet, Jean-François, Hamon, Jean-René, Lapinte, Claude
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.08.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Subjects: Accessibility; Chemical Sciences; Chemistry; Chemistry, Inorganic & Nuclear; Conjugated systems; Electron paramagnetic resonance; Electron spin; Electron transfer; Hybrid materials; Infrared spectroscopy; Iron; Isomers; Mixed-valent compounds; Molecular electronics; or physical chemistry; Physical Sciences; Precursors; Science & Technology; Theoretical and; Tunneling; IRON SIGMA-ACETYLIDES; MOLECULAR WIRES; SPECTROSCOPIC PROPERTIES; Iron; ELEMENTAL CARBON-CHAIN; Molecular electronics; ORDER REGULAR APPROXIMATION; NONLINEAR-OPTICAL PROPERTIES; Mixed-valent compounds; ELECTRON-TRANSFER RATES; FUNCTIONAL ARYL GROUP; X-RAY CRYSTAL; CHARGE-TRANSFER; Hybrid materials; Conjugated systems
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201402022

The organic precursor bis(trimethylsilylethynyl)TTFMe2 (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* = 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 mixture 6‐cis/trans (63 %), respectively. The oxidation of 6‐trans with [(C5H5)2Fe]PF6 gave [6‐trans][PF6]n (n = 1–3). Visible, IR, near‐IR (NIR), and electron paramagnetic resonance (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 molecule. Intramolecular electron transfer occurs through single‐step tunneling and a multistep hoping mechanism. The triplet state is thermally accessible for [6‐trans][PF6]2. The complex trans‐[Cp*(dppe)Fe–C≡C–TTFMe2–C≡C–Fe(dppe)Cp*][PF6] [Cp* = η5‐C5Me5, dppe = 1,2‐bis(diphenylphosphanyl)ethane, TTF = tetrathiafulvalene] is a class II mixed‐valence compound in which the spin density varies with the respective orientation of the metal termini. Intramolecular electron transfer occurs through single‐step tunneling and multiple‐step hopping mechanisms.