Abstract
AbstractThe 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 characterised by alternate layers of tetrahedral and octahedral FeIII 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 0.4 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], bulk iron oxides, previous FeIII–oxo cages, and polyoxometalates (POMs), hints that much larger molecular FeIII oxides can be made.
Highlights
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 characterised by alternate layers of tetrahedral and octahedral Fe(III) ions connected by oxide and hydroxide ions
Fascinating physical properties - the high symmetry icosidodecahedron possessing geometric spin frustration.[7]. This has prompted us to speculate that large and very large Fe(III) molecular metal oxides, approaching the size and structural diversity of POMs, can be constructed, but with the terminal oxides replaced by simple monodentate ligands
The most pertinent examples of Fe(III) clusters conforming to POMlike architectures are [Fe13][4] and [Fe17];[5] both are structurally related with alternating layers/shells of tetrahedral and octahedral metal ions - the former has the α-Keggin structure,[4a] and the latter the ε-Keggin structure with four additional capping metal ions.[5]
Summary
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 characterised by alternate layers of tetrahedral and octahedral Fe(III) ions connected by oxide and hydroxide ions. In POM chemistry the addition of (bulky) organic amine cations is thought to aid the selfasembly of large nuclearity species by isolating the smaller building blocks, preventing rapid aggregation into complexes with (smaller) stable spherical topologies.[10] we discuss the synthesis, structure and magnetic behaviour of [FeIII34(μ4-O)4(μ3O)34(μ2-OH)12Br12(py)18]Br2 (1) (Figure 1, S1-S5) which is made via just such a strategy, through a small modification (the addition of either hexamethylene tetramine (HMTA) or morpholine) in the preparation of [Fe17].[11]
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