Syntheses, crystal structures, spectroscopic and magnetic properties of two trinuclear iron complexes with carboxylate and oximate mixed-bridge ligands

Two trinuclear oxo-centered iron(III) complexes [Fe-3(mu (3)-O)Salox(L1)(5)(MeOH)(2)] (1) and [Fe-3(mu (3)-O)Salox(L1)(5)(EtOH)(2)]center dot 2EtOH center dot 2H(2)O (2) (Salox = salicylaldoxime, L1 = o-nitrobenzoic acid) have been synthesized, and their X-ray crystal structures, spectroscopic properties (IR, UV-Vis, fluorescence), and magnetic properties have been characterized. In each complex, the three Fe(III) centers of the [Fe3O] moieties are joined together by a mu (3)-O unit to form an isosceles triangle, and each metal center has a distorted octahedral coordination geometry. The fluorescence emission intensities for the two complexes are much higher than those of the free proligands, suggesting that the [Fe3O] structural unit increases the rigidity of the ligands after coordination, and the enlarged conjugate system reduces the frontier orbitals energy gap. The nature of magnetic coupling within complexes 1 and 2 indicates both intramolecular strong and intermolecular weak antiferromagnetic interactions.