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Unusually strong antiferromagnetic coupling in unsymmetrical diiron(III) μ-oxo complexes

AuthorsGómez-Romero, P. ; Jameson, Geoffrey B.
Issue Date1990
PublisherAmerican Chemical Society
CitationInorganic Chemistry 29(26): 5211-5217 (1990)
AbstractThe complex [N6FeOFeCl3]Cl·0.5HCl·3H2O·2C 2H5OH, where N6 is the potentially hexadentate ligand N,N,N′,N′-tetrakis((2-benzimidazolyl)methyl)ethanediamine, shows distinctively strong antiferromagnetic coupling (J = -126 (1) cm-1), more typical of multiply bridged diiron(III) μ-oxo species than of singly bridged species. The X-ray crystal and molecular structure shows a single oxo bridge linking an octahedrally coordinated Fe(III) - one benzimidazole group of ligand N6 does not coordinate - with a tetrahedrally coordinated Fe(III). Some key metrical details are as follows: O-FeCl3, 1.745 (7) Å; O-FeN6, 1.791 (7) Å; Fe-O-Fe, 153.2(4)°; average Fe-Cl 2.20 (1) Å; average Fe-NIm, 2.08 (2) average Fe-Namine, 2.32 (4) Å. Infrared spectroscopy reveals a strong doublet at 833 and 850 cm-1 that is associated with the Fe-O-Fe moiety; the latter band is assigned to vas(Fe-O-Fe). An analysis of orbital interactions reveals how low symmetry (at most, idealized Cs) can facilitate stronger antiferromagnetic coupling than occurs for more symmetrical (C2v) singly bridged diiron(III) μ-oxo species. The distinctive magnetic and vibrational properties associated with these unsymmetrical species extends the range of spectroscopic behavior associated with diiron(III) μ-oxo species, with important consequences in the application of these techniques to dinuclear iron proteins. Relevant crystal and refinement data include the following: monoclinic space group P21/n; a = 13.775 (4), b = 26.911 (7), c = 13.758 (4) Å; β = 96.24 (2)° dobs = 1.28 (2), dcalc = 1.29 g cm-3 for Z = 4; 4231 retained data with I > 0 in the range 0.10 < λ-1 sin θ < 0.5399 Å-1; graphite-monochromated Mo Kα radiation (γ = 0.7107 Å); R(F2, all data) = 0.19, Rw(F2) = 0.22; for the 2126 data for which I > 3σ(I), R(F) = 0.088 and Rw(F) = 0.104.
Identifiersdoi: 10.1021/ic00351a015
issn: 0020-1669
e-issn: 1520-510X
Appears in Collections:(ICMAB) Artículos
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