An ‘Empty’ [Fe 16 ] Cage and its Transformation into [Fe 17 ] and [Fe 30 ]

Abstract

ABSTRACT Polymetallic clusters of Fe III constructed without organic bridging ligands are an emerging class of molecules with structures akin to iron oxide minerals, possessing large spin ground states and/or displaying spin frustration effects. All previous examples, [Fe 8 ], [Fe 17 ], [Fe 30 ] and [Fe 34 ], have been isolated from pyridine or analogous heterocyclic amine solvents. Here, we report the isolation of an [Fe 16 ] cluster from dmf. The complex is ‘isostructural’ with the previously reported [Fe 17 ] molecular metal oxide, but with the central, tetrahedral Fe III ion absent. Antiferromagnetic exchange interactions between the tetrahedral and octahedral Fe III ions in [Fe 16 ] lead to a spin ground state of S = 20, the highest yet for this family of materials, consistent with the S = 35/2 found for [Fe 17 ] containing an additional (antiferromagnetically coupled) s = 5/2 ion. Dissolution of [Fe 16 ] in pyridine regenerates [Fe 17 ] or the larger [Fe 30 ], depending on reaction conditions, demonstrating for the first time that these species can be interconverted.