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Iron(II) Complexes Based on π-Conjugated Terpyridine Ligands with Tetrathiafulvalene or Its Radical Analogue



Two tetrathiafulvalene (TTF) functionalized 2,2′:6′,2″-terpyridine derivatives, 4′-tetrathiafulvalene-2,2′:6′,2″-terpyridine (L1) and 6,6″-dimethyl-4′-tetrathiafulvalene-2,2′:6′,2″-terpyridine (L2), were synthesized and characterized. Based on L1 and L2, four electrochemically active TTF-containing iron(II) complexes, [FeII(L1)2][ClO4]2 (1), [FeII(L1·+)2][ClO4]4 (2), [FeII(L1)2][CF3SO3]2 (3) and [FeII(L2)2][ClO4]2 (4), were successfully obtained. The preparation, spectroscopic and electrochemical properties of these new compounds as well as the crystal structures of complexes 1, 3 and 4 are described. Magnetic studies on 4 (with the ligand L2) suggest that the FeII ion is in the high-spin state. Complex 2 was isolated as an interesting and stable open-shell substance, and the free spin is mainly associated with the TTF radicals, as indicated by EPR, UV/Vis spectra, electrochemical analysis, spectroelectrochemical measurements and XPS spectra. After the oxidation and the formation of the radical cation, the electrical conductivity of 2 is almost 3 orders of magnitude higher than that of 1. DFT and TDDFT calculations provided insight into interpreting the electronic properties of complex 1 and its oxidized states.