Synthesis and characterisation of Fe6 and Fe12 clusters using bicine

Reaction of bicine {BicH3, N,N-bis(2-hydroxyethyl)glycine} with an Fe(III) oxo-centered pivalate triangle in MeCN in the presence of Et2NH yields [Et2NH2]2[Fe6O2(OH)2(Bic)2(O2CCMe3)8], which possesses an S = 5 ground state. Changing the base to NaOMe produces [Fe12O4(Bic)4(HBic)4(O2CCMe3)8], which contains two Fe6 units bridged by the carboxylate arms from the bicine ligands. The complex displays strong antiferromagnetic coupling leading to an S = 0 ground state. 2009 Elsevier Ltd. All rights reserved. Polymetallic transition metal complexes continue to attract intense interest in the field of molecular magnetism [1,2]. Alongside the potential applications in high-density data storage, there are opportunities in quantum computation [3], MRI contrast agents [4], magnetic refrigeration [5], and spintronics [6]. One strand of our research focuses upon the coordination chemistry of a series of structurally related ligands with the first row transition metal ions. We are investigating the substitution of functional groups on a given ligand backbone and how this affects the topology of the clusters that crystallise from the reaction system. This approach can be illustrated by Chart 1, which shows the ligands bis–tris, bicine {BicH3, N,N-bis(2-hydroxyethyl)glycine} and diethanolamine (DEA), which all share the {N(CH2CH2OH)2} group. We have shown that bis–tris can assemble small fragments of iron(III) carboxylates into Fe10 clusters [7]. Although the DEA ligand has not been reported as a ligand for Fe(III) complexes, replacing the NH group by an NR (R = Me, Et etc.,) group leads to some interesting polynuclear Fe(III) complexes, including Fe6 wheels (e.g. R = Me [8], Bu [9]) and in the presence of carboxylate co-ligands Fe7 or Fe22 complexes (R = Ph [10] or Me [11]). As bicine contains a carboxylate group in addition to the {N(CH2CH2OH)2} functionality this ligand should form new and interesting polynuclear Fe(III) clusters. However, the only reported polynuclear complex with the bicine ligand is a hexa-nuclear [Fe6(Bic)6] wheel [12] where each bicine ligand is tri-deprotonated. Previously, mono-deprotonated bicine has been ll rights reserved. x: +44 141 330 4888.