A triiron complex containing the carboxylate-free {Fe < inf > 3 < /inf > (μ < inf > 3 < /inf > -O)} < sup > 7+ < /sup > core and distorted pentagonal-bipyramidal metal centres

Abstract

The reaction of Fe(ClO4)3·6H2O, 1,2-bis(biacetylmonoximeimino)ethane (H2bamen) and triethylamine (1:1:2 mol ratio) in methanol affords a trinuclear complex with the formula [Fe3(μ3-O)(μ3-bamen)3]ClO 4·2H2O. The structure of the complex cation in this species shows a symmetric planar central {Fe3(μ3-O)} 7+ unit coordinated to three N4O2 donor bridging (via oximate groups) ligands (bamen2-). The N 4O3 coordination sphere around each metal centre is very close to pentagonal-bipyramidal. Four N atoms of one bamen2- and the oxo group satisfy five coordination sites and form a pentagonal plane around the metal ion. The axial sites are occupied by two oximato O atoms from the other two bamen2- ligands. Thus, in addition to the μ3-oxo group, two oximate groups provide two additional bridges between each pair of metal centres. In the crystal lattice, the water molecules exist as hydrogen-bonded dimers and these water dimers together with the perchlorate ions form a hydrogen-bond-supported helix. The complex cations form a chain via C-H⋯O interactions involving a methyl group and a metal-coordinated oximato O atom. The helix of {(H2O)2ClO4-} units and the chain of [Fe3O(bamen)3] + cations are connected by O-H⋯O interactions which involve a water molecule and a second oximato O atom. In its cyclic voltammogram, the complex displays metal-centred oxidation as well as reduction responses. Variable-temperature magnetic susceptibility measurements revealed the presence of an antiferromagnetic interaction [J = -41.0(2) cm-1] between the FeIII centres in this complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).