The molecular and electronic structure of symmetrically and asymmetrically coordinated, non-heme iron complexes containing [FeIII(μ-N)FeIV]4+ (S = 3/2) and [FeIV(μ-N)FeIV]5+ (S = 0) cores

Thomas Jüstel, Michael Müller, Thomas Weyhermüller, Claudia Kressl, Eckhard Bill, Peter Hildebrandt, Marek Lengen, Michael Grodzicki, Alfred X. Trautwein*, Bernhard Nuber, Karl Wieghardt

*Corresponding author for this work
51 Citations (Scopus)


Photolysis of [LFeIII(nadiol)(N3)] (2) in dry CH3CN at 20 °C produces red-brown crystals of the dinuclear symmetrically coordinated complex [{L(nadiol)Fe}2(μ-N)] (6) in 40% yield (L = 1,4,7-trimethyl-1,4,7-triazacyclononane and nadiol2- = naphthaline-2,3-diolate). One-electron oxidation of 6 in dry CH2Cl2 with one equivalent of ferrocenium hexafluorophosphate generates blue crystals of {(L(nadiol)-FeIV}2(μ-N)]PF6 (7). Photolysis of an equimolar CH3CN solution of [L(Ph2acac)FeIII(N3)]ClO4 (3) (Ph2acac- is the monoanion 1,3-diphenylpropane-1,3-dionate) and [L(Cl4-cat)FeIII(N3)] (Cl4-cat2- = tetrachlorocatecholate dianion) produces the asymmetrically coordinated species [L(Ph2acac)-FeIII=N=FeIV(Cl 4-cat)L]ClO4 (8) in 50% yield. The (μ-oxo)diferric complexes [{L(acac)FeIII}2(μ-O) ](ClO4)2 (4) (acac- = pentane-2,4-dionate) and [{L(nadiol)FeIII}2(μ-O)] (5) have also been prepared for comparison with complexes 6-8. Complexes 4-8 have been characterized by single-crystal X-ray crystallography. Complexes 6 and 8 contain mixed-valent [FeIV- (μ-N)FeIII]4+ cores, whereas 7 contains the linear, symmetric [FeIV(μ-N)FeIV]5+ core with an FeIV-Nb bond length of 1.694(1) Å. The FeIII-Nb bond length of 1.785(7) Å in 8 is longer than the FeIV-Nb bond length of 1.695(7) Å at 100 K (Δ = 0.09 Å). The electronic structure of these complexes has been characterized by Mössbauer, electron paramagnetic resonance (EPR), resonance Raman (RR) and UV/Vis spectroscopy, electrochemistry and magnetic susceptibility measurements, and by molecular orbital calculations by local density approximation. These studies reveal that 4 and 5 contain two equivalent highspin FeIII ions which exhibit the usual antiferromagnetic coupling of the [FeIII(μ-O)FeIII]4+ core (J = - 90 and - 95cm-1) to a diamagnetic ground state. Similarly, 7 is diamagnetic even at room temperature and contains two equivalent FeIV ions, which are strongly antiferromagnetically coupled to also yield an S = 0 ground state. On the other hand, complexes 6 and 8 display an S = 3/2 ground state and two nonequivalent, strongly antiferromagnetically coupled iron sites with partially delocalized valencies. Therefore, a description of the [Fe(μ-N)Fe]4+ core as containing a highspin ferric ion (S = 5/2) and a low-spin ferryl ion (S=1) has formal character only.

Original languageEnglish
JournalChemistry - A European Journal
Issue number2
Pages (from-to)793-810
Number of pages18
Publication statusPublished - 01.01.1999


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