Giant Spin Structures

 

Introduction. We have prepared hexanuclear iron clusters supported by tris(o-phenylenedimaine)-based ligands which feature large spin ground states up to S = 11. Uniquely, these large spin ground states are well-isolated from excited states up to room temperature, allowing the clusters to behave as single giant spins. This makes them an ideal target for studies of molecular magnetism and molecule-based magnetic materials.

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Synthesis and structure. Unlike most metal clusters, which are often prepared by complex and unpredictable self-assembly reactions, these hexanuclear iron clusters assemble via a straightforward dimerization of two trinuclear (XL)Fe   fragments, yielding the formulation (XL) Fe  . Notably, the clusters feature iron centers with unusual square planar coordination geometries, allowing the open axial coordination sites to serve as handles for manipulating the magnetism and the topology of the clusters.

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Electronic and magnetic properties. Relatively short Fe‒Fe contacts (typically 2.50 to 2.75 Å) allow electronic communication between the metal centers. Strong electronic delocalization occurs in mixed-valent oxidation states, allowing up to six different oxidation states to be observed electrochemically, spanning a 4 V window. Reduction of the clusters triggers strong double exchange, causing the spin state to increase dramatically from S = 6 in the neutral state to S = 19/2 in the anionic state. Additionally, the anionic clusters behave as single-molecule magnets at low temperatures.

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Future directions. Future work will focus on the preparation of magnetic solids incorporating these clusters as giant-spin building blocks, in addition to characterizing the details of their unique magnetic behavior using advanced spectroscopic and diffraction techniques. These studies will lead to new insights in the fundamentals of molecular magnetism as well as potential applications in magnetic and electronic materials.