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

Abstract

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.

Towards the Molecular Design of Spin‐Crossover Complexes of 2,6‐Bis(pyrazol‐3‐yl)pyridines

“… R‐Disubstituted tridentate ligands in the previously reported iron(II) complexes: 1‐bpp with R=methyl (Me), phenyl (Ph), iso ‐propyl ( i Pr), ethoxycarbonyl (CO 2 Et), hydroxymethyl (CH 2 OH), ferrocenyl (FeCp 2 ), and mesityl (Mes) groups; 3‐bpp with R=methyl (Me), phenyl (Ph), iso ‐propyl ( i Pr), benzyl (Bz) and allyl (All) groups; 1,3‐bpp and terpy with R=phenyl (Ph), 4‐methoxyphenyl (Ph−4‐OMe), p ‐tolyl (pTol) and methyl (Me) groups, bromine (Br), chlorine (Cl) and fluorine (F) atoms. An inset: ligands L R in this study with R=fluorine (F), chlorine (Cl), methyl (Me), ethyl (Et) and iso ‐propyl ( i Pr) substituents; L H was reported earlier …”

Luminescence and Single‐Molecule‐Magnet Behaviour in Lanthanide Coordination Complexes Involving Benzothiazole‐Based Tetrathiafulvalene Ligands

“…[23,30] Historically, TTF derivatives have been used for their donating abilities, which can lead to electronic conductivity. [31] A fruitful strategy is to add localized electrons to the TTF core from transition metals (3d and 4d) [32][33][34][35][36][37] or lanthanides. [30,38] Such π-d and π-f systems have shown exciting transport properties such as antiferromagnetic-superconductor or magnetic-field-induced superconducting transitions.…”

Ambivalent binding between a radical-based pincer ligand and iron

“…The general approach has been to replace the peripheral pyridine rings with nitrogen rich functional groups, or to attach radical pendant groups to the central pyridine ring at the 2, 4 and/or 6 positions. [23][24][25][26][27] Although this has afforded ligands that offer improved redox activity compared to terpy, their application remains limited due to reduction potentials, solubility and stability of the isolated metal complexes. Alternatively, an inherently redox active structural mimic of terpy may be achieved by exchanging the three carbon atoms within the central pyridyl ring with the N-S-N fragment leading to 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazinyl (Py 2 TTA • ), a neutral seven π-electron ring system flanked by two pyridyl groups.…”