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 [Fe34] metal oxide molecule, structurally characterized by alternate layers of tetrahedral and octahedral Fe(III) ions connected by oxide and hydroxide ions. The outer shell of the cage is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, 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 [Fe34], iron oxides, previous Fe(III)-oxo cages, and polyoxometalates (POMs), hints that much larger, molecular Fe(III) oxides can be made.