An [FeIII34] Molecular Metal Oxide

The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe-34] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral Fe-III ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4K and fields up to 35T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe-O-Fe angles and Fe-O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe-34], bulk iron oxides, previous Fe-III-oxo cages, and polyoxometalates (POMs), hints that much larger molecular Fe-III oxides can be made.