A planar carboxylate-rich tetrairon(II) complex and its conversion to linear triiron(II) and paddlewheel diiron(II) complexes

Erwin Reisner, Joshua Telser, Stephen J. Lippard

    Research output: Contribution to journalArticlepeer-review


    We report a series of oligonuclear carboxylate-rich high-spin iron(II) complexes with three different [FeIIn(μ-O 2Cbiph)2n(L)m] (n = 2-4; m = 2 or 4) structural motifs, where _O2Cbiph is 2-biphenylcarboxylate and L is an exogenous ligand bound to terminal iron atoms. Solid compounds were isolated and their structural, spectroscopic, and magnetic properties thoroughly investigated. The discrete tetranuclear complexes [Fe4(μ-O 2Cbiph)8(L)2] crystallize in a planar tetrairon(II) motif in which two diiron paddlewheel units are linked in an unprecedented manner involving a μ3-1,1,3-bridging mode. X-ray crystallography reveals average Fe-Oanti bond lengths of 2.081 [2] Å at the dimer-dimer interface. Terminal axial positions are capped by ligands L, where L is tetrahydrofuran (THF) (1), indazole (2), pyrazole (3), 3,5-dimethylpyrazole (4), or acetamide (5). Reaction of 1 with an excess of acetonitrile affords the linear compound [Fe3(μ-O 2Cbiph)6(MeCN)4] (6). The acetonitrile ligands in 6 can be replaced by THF or dimethoxyethane at elevated temperatures with retention of the structure to afford 7 and 8, respectively. Reaction of 1 or 6 with pyridine or 1-methylimidazole results in the isolation of paddlewheel dimers 9 and 10, respectively, with [Fe2(μ-O2Cbiph) 4(L)2] composition. Mössbauer spectroscopy confirms the presence of high-spin ferrous ions and indicates that the two iron sites of the dimer are geometrically indistinguishable. For the tri- and tetrairon compounds, two quadrupole doublets are observed, suggesting that the iron centers do not have identical geometries. Plots of magnetic susceptibility versus temperature reveal intramolecular antiferromagnetic exchange coupling for all complexes under study. The magnetic data were fit to a theoretical model incorporating exchange coupling, single-ion zero-field splitting, and g-tensor anisotropy. The resulting magnetic parameters reveal in most cases weak antiferromagnetic exchange coupling (J typically
    Original languageEnglish
    Pages (from-to)10754-10770
    Number of pages16
    JournalInorganic Chemistry: including bioinorganic chemistry
    Issue number25
    Publication statusPublished - 10 Dec 2007


    • Mossbauer effect (in iron biphenylcarboxylate complexes)
    • Antiferromagnetic exchange
    • Crystal structure
    • Ferromagnetic exchange
    • Magnetic susceptibility
    • Molecular structure
    • Oxidation
    • Oxidation potential
    • Reduction
    • Reduction potential (of iron biphenylcarboxylate complexes)
    • iron biphenylcarboxylate complex prepn structure
    • electrooxidn iron biphenylcarboxylate complex
    • electroredn iron biphenylcarboxylate complex
    • crystal structure iron biphenylcarboxylate complex
    • magnetic property iron biphenylcarboxylate complex
    • Mossbauer iron biphenylcarboxylate complex


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