A T‐Shaped μ3‐Oxido Trinuclear Iron Cluster with High Easy‐Plane Anisotropy: Structural and Magnetic Characterization

Abstract

AbstractThe 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 Å, c = 37.3538 Å, Z = 8, V = 6941.7 Å3). 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)