A trinuclear cluster containing the {Fe3(μ3-O)7+ core:: Structural, magnetic and spectroscopic (IR, Mossbauer, EPR) studies

A ferric complex, [Fe3O(O2CPh)(6)(EtOH)(2)(N-3)]- 2.4EtOH (1-2.4EtOH) has been synthesized through the reaction of basic iron benzoate with NaN3. It crystallizes in the C2/c space group and it contains a planar {Fe-3(mu(3)-O)}(7+) core typical of basic iron carboxylates. Mossbauer spectra above 80 K display asymmetric quadrupole-split doublets that are consistent with the existence of two iron sites with O-6 and O5N environments in a 2:1 ratio, respectively. Below 80 K the linewidth increases and the asymmetry vanishes. Variable-temperature magnetic susceptibility studies reveal the interplay of antiferromagnetic interactions, which require a 2J model for their interpretation (two equal J and one different J ' exchange constants). The fitting process yields two minima (J = -26.4 cm(-1), J ' = -40.0 cm(-1) and J = -33.0 cm(-1), J ' = -24.0 cm(-1) for a H= -2 Sigma J(ij)S(i)S(j) spin Hamiltonian formalism), both of which lead to S = 1/2 ground states. Solid-state EPR measurements corroborate the existence of an S = 1/2 ground state, also indicating weak intermolecular interactions leading to broadened signals. (c) 2005 Elsevier Ltd. All rights reserved.