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RESEARCH PRODUCT

A T‐Shaped μ 3 ‐Oxido Trinuclear Iron Cluster with High Easy‐Plane Anisotropy: Structural and Magnetic Characterization

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The synthesis, crystal structure and magnetochemical characterization of a new μ-oxido trinuclear iron cluster (oldnomenclature: μ-oxo trinuclear iron cluster), [Fe3(μ3-O)(μ2-CH3O)2(μ2-CH3COO)2(phen)2Cl3], is reported. The reaction of hydrated FeCl3 with sodium acetate and 1,10-phenanthroline in a mixture of methanol and acetonitrile afforded crystals suitable for X-ray crystallographic determination. The new compound crystallizes in the tetragonal I41/a space group (a = b = 13.6322 A, c = 37.3538 A, Z = 8, V = 6941.7 A3). The core of the complex is an isosceles triangle bridged by a μ3-O ion with a rare T-shaped geometry. The chloride ions are bound terminally, and the phenanthroline ligands are π-stacked. Variable-temperature solid-state dc magnetization studies were carried out in the 2.0–300 K range. Data were fit with an isotropic Heisenberg spin Hamiltonian, which included an axial anisotropy (zero-field splitting) term. Two antiferromagnetic exchange parameters for the isosceles triangle arrangement of the iron ion were needed, with values of –11.2 and –47.7 cm–1, while a positive D value of about 1.5 cm–1 was obtained. In addition, magnetization (M) vs. field (H) and temperature (T) data established an ST = 5/2 ground-state spin. We also performed broken-symmetry DFT calculations, which reproduced the experimental J values and the ground-state spin well. The replacement of one Fe3+ ion by a Ga3+ ion allowed for simplification of the three-centre problem to one treating a dinuclear exchange-coupled system, and this afforded good computed values. To the best of our knowledge, this is the first time that this specific replacement has been applied within broken-symmetry DFT calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)