A Triiron Complex Containing the Carboxylate‐Free {Fe3(μ3‐O)}7+ Core and Distorted Pentagonal‐Bipyramidal Metal Centres

Abstract

AbstractThe 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]ClO4·2H2O. 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 N4O3 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)