A T-shaped mu(3)-oxido trinuclear iron cluster with high easy-plane anisotropy: Structural and magnetic characterization

ALBORÉS PABLO; EVA RENTSCHLER

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

Wiley-VCH

Año: 2008 p. 4004 - 4011

1434-1948

The synthesis, crystal structure and magnetochemical characterization of a new p-oxido trinuclear iron cluster (old nomenclature: [mu-oxo trinuclear iron cluster), [Fe-3(mu(3)-O)(mu(2)-CH3O)(2)(mu(2)-CH3COO)(2)(phen)(2)Cl-3], 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 I4(1)/a space group (a = b = 13.6322 angstrom, c = 37.3538 angstrom, Z = 8, V = 6941.7 angstrom(3)). The core of the complex is an isosceles triangle bridged by a mu(3)-O ion with a rare T-shaped geometry, The chloride ions are bound terminally, and the phenanthroline ligands are pi-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 S-T = 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.