A Mixed-Valence Fluorido-Bridged Fe^IIFe^III Complex

Abstract

The reaction of the new dinucleating ligand susan with Fe(BF)·6HO results in formation of the homovalent FeFe complex [(susan){Fe(μ-F)Fe}] and the mixed-valence FeFe complex [(susan){FeF(μ-F)FeF}] depending on the absence or presence of dioxygen, respectively. Complex [(susan){FeF(μ-F)FeF}] is the first molecular mixed-valence complex with a fluorido bridge. The short Fe-μ-F bond of 1.87 Å causes a large reorganization energy, resulting in a localized class II system with an intervalence charge-transfer band of high energy at 10000 cm.

Electron Delocalization of Mixed‐Valence Diiron Sites Mediated by Group 10 Metal Ions in Heterotrimetallic Fe‐M‐Fe (M=Ni, Pd, and Pt) Chain Complexes

“…Slight differences of d (Fe−M central ), d (Fe−Cl), and d (Fe−N) for both complexes are observed, Δ d =0.01≈0.02 and 0.02≈0.03 Å for [ 1 ] + and [ 3 ] + , respectively, compared with the corresponding values in the other heterovalent diiron complexes that showed the distinguishable changes about the Fe II /Fe III coordination parameters. A significant difference of the Fe−F distances, Δ d =0.29 Å, was found in a fluorido‐bridged charge‐localized hetero‐valent complex [(susan 6‐Me )‐{Fe II F(μ‐F)Fe III F}] 2+ (susan 6‐Me =4,7‐dimethyl‐1,1,10,10‐tetra(6‐methyl‐2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane) . Moreover, Que et al.…”

“…susan 6-Me = 4,7-dimethyl-1,1,10,10-tetra(6-methyl-2pyridylmethyl)-1,4,7,10-tetraazadecane). [24] Moreover,Q ue et al reportedt he valence-localized nature of {Fe II (m-O)Fe III }a nd {Fe II (m-OH 2 )Fe III }c ores exhibiting discrete Fe II and Fe III centersi n biomimetic oxo-o rh ydroxo-bridged non-heme diiron complexes. [25] These two iron sites manifest distinct d(FeÀO) lengths with variations in the range of 0.15-0.19 .T herefore, we tentatively assign the two iron centers in [1] + and [3] + are indistinguishable.…”

Reactivity Differences for the Oxidation of FeIIFeII to FeIII(µ‐O)FeIII Complexes Caused by Pyridyl versus 6‐Methyl‐Pyridyl Ligands

“…However, although these complexes exhibit low redox potentials for oxidation, the oxidations are ligand‐centered leading to coordinated phenoxyl radicals and the oxidized dinuclear complexes decay into mononuclear fragments , . Thus, we have developed a dinucleating bis(tetradentate) ligand system to coordinate a {Fe(µ‐O) 2 Fe} core (Schemeà) employing different terminal donors (carboxylates, phenolates, and pyridines) , , . The strong electron‐donating character of the bis‐µ‐oxo bridge should enable the oxidation to high‐valent species.…”

“…To evaluate the influence of a 6‐methyl group in the pyridine donors as in tpa vs tpa 6‐Me , we synthesized the ligand susan 6‐Me (Schemeà) . Due to the ease in the synthesis of [(susan){Fe III Cl(µ‐O)Fe III Cl}] 2+ , we tried first the synthesis of the related complex [(susan 6‐Me ){Fe III Cl(µ‐O)Fe III Cl}] 2+ but were unable to generate this complex despite severe efforts.…”

“…The reaction with susan under basic aerobic conditions proceeds smoothly to the oxo diferric complex [(susan){Fe III F(µ‐O)Fe III F}](BF 4 ) 2 with terminal fluorido ligands. The analogous reaction with susan 6‐Me does not yield [(susan 6‐Me ){Fe III F(µ‐O)Fe III F}] 2+ but the mixed‐valence complex [(susan 6‐Me ){Fe II F(µ‐F)Fe III F}](BF 4 ) 2 by reaction under exposure to air and the diferrous complex [(susan 6‐Me ){Fe II F(µ‐F)Fe III F}](BF 4 ) 2 without exposure to air . To obtain [(susan 6‐Me ){Fe III F(µ‐O)Fe III F}] 2+ , H 2 O 2 has to be added to the reaction mixture.…”