Synthesis and Characterization of Neutral Hexanuclear Iron Sulfur Clusters Containing Stair-like [Fe63-S)42-SR) 4] and Nest-like [Fe63S)22-S) 24-S)(μ2SR)4] Core Structures 1

Frank Osterloh*, Wolfgang Saak, Siegfried Pohl, Monika Kroeckel, Christian Meier, Alfred X. Trautwein

*Corresponding author for this work
11 Citations (Scopus)


Dedicated to Professor Achim Müller on the occasion of his 60th birthday. The binuclear iron complex [{Fe("EtN2S2")}2] (1b, "EtN2S2" = N,N'-diethyl-3,7-diazanonane-1,9-dithiolate) was prepared from the free ligand and ferrous bis[bis(trimethylsilyl)amide] in toluene. In dichloromethane 1b reacts with the [Fe4S4I4]2- cubane cluster to displace two iodo ligands and to form the neutral hexanuclear cluster [{Fe("EtN2S2")}2Fe4S 4I2] (2), which is isolated as black crystals in 87% yield. As elucidated by an X-ray structure analysis, 2 contains the novel hexanuclear stair-like [Fe63-S)42-SR) 4] core, which exhibits crystallographic inversion symmetry. The compound crystallizes as a solvate with two molecules of CH2Cl2 per formula unit in the monoclinic space group F21ln with a = 1570.5(2) pro, b = 1060.2(1) pm, c = 1604.0(2) pm, β= 114.93(1)°, and Z = 2. In the aprotic polar solvents DMF, 1,2-propylenecarbonate, and DMSO, 2 dissolves with decomposition and formation of the cluster [{Fe("EtN2S2")}2Fe4S 5] (3), which is isolated as black needles from DMF. 3-2DMF crystallizes in the triclinic space group P1 with a = 950.9(1) pm, b -1086.0(1) pm, c = 2381.5(2) pm, α = 101.81(1)°, β= 91.94(1)°, γ = 97.01(1)°, and Z = 2. The neutral compound contains a nest-like [Fe64-S)(μ3-S)22-S)22-SR)4] core of idealized C2v symmetry that is closely related to that of other well-known clusters, e.g., the cluster anion [Fe6S9(SR)2]4-. The zero-field 57Fe Mössbauer spectrum of 3 is in accordance with four Fe2.5+S4 centers (δ = 0.46 mm/s; ΔEQ =1.14 mm/s) and two N2S3-bound high-spin Fe2+ sites (δ=0.83 mm/s; ΔEq = 3.64 mm/s). A total cluster spin of 0 is deduced from the Mössbauer spectrum at 4.2 K and 5.3 T, which yields magnetic splitting from the applied field only. For 2, three subspectra are observed in the Mössbauer spectrum (a, δ= 0.45 mm/s, ΔEq = 1.05 mm/s; b, δ= 0.55 mm/s, ΔEQ =1.61 mm/s, c, δ= 0.80 mm/s; ΔEQ = 3.83 mm/s) reflecting different coordination environments of the iron atoms rather than different oxidation states. The electrochemical properties of 1b, 2, and 3 were determined by cyclic voltammetry. 1b can be quasireversibly oxidized in dichloromethane solution at -75 mV (vs SCE). Whereas 2 shows only an irreversible redox behavior in N,N'-dimethylirnidazolidin-2-one solution, 3 in the same solvent can be quasi-reversibly reduced in two consecutive steps at -830 and -1630 mV (vs SCE) to the dianion, which consists entirely of Fe(II).

Original languageEnglish
JournalInorganic Chemistry
Issue number14
Pages (from-to)3581-3587
Number of pages7
Publication statusPublished - 24.06.1998


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