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 (L 1 ) and 6,6″‐dimethyl‐4′‐tetrathiafulvalene‐2,2′:6′,2″‐terpyridine (L 2 ), were synthesized and characterized. Based on L 1 and L 2 , four electrochemically active TTF‐containing iron(II) complexes, [Fe II (L 1 ) 2 ][ClO 4 ] 2 ( 1 ), [Fe II (L 1 · + ) 2 ][ClO 4 ] 4 ( 2 ), [Fe II (L 1 ) 2 ][CF 3 SO 3 ] 2 ( 3 ) and [Fe II (L 2 ) 2 ][ClO 4 ] 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 L 2 ) suggest that the Fe II 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.