Directed Assembly of Molecular Cluster Magnets

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This award in the Inorganic, Bioinorganic and Organometallic Chemistry program to Professor Jeffrey R. Long of the University of California at Berkeley is to develop general strategies for the synthesis of metallocyanide coordination clusters as single-molecule magnets (SMMs) that have potential in high-density information storage and quantum computing. The ability to utilize organic blocking ligands in directing the formation of specific metallocyanide cluster geometries will be extended to the synthesis of higher-nuclearity species, such as edge-centered cubic [(L-fac)8(Leq) 12M12M'8(CN)24]n+ and double-cube [(L-fac)14M7M'8(CN)24]n+ clusters. The substitution of appropriate paramagnetic metal ions into these clusters has led to ground states of up to S = 18, and new species with spins as high as S = 32 will be targeted. Incorporation of metal ions possessing a large axial zero-field splitting into such structures will be pursued as a means of generating the magnetic anisotropy requisite of a single-molecule magnet. Additional work will focus on further enhancing magnetic anisotropy through the incorporation of third-row transition metal centers bearing orbital angular momentum, such as Ta(III), W(IV), Re(III), Re(V), and Os(IV). Moreover, the use of heavy donor atom ligands will be tested as a means of further increasing the single-ion anisotropy associated with cluster building units. Routes to linear clusters with parallel alignment of the individual ion anisotropy axes are proposed, as is a method for breaking the symmetry in high-nuclearity cubic species via heterometal substitution. A magnetochemical series in which linear bridging ligands are ordered according to their magnetic exchange coupling ability, will be established as a means of evaluating replacement ligands for cyanide with stronger magnetic coupling. In addition, certain of these ligands may facilitate electron transfer to an extent that enables the synthesis of mixed-valent, ligand-bridged clusters with well-isolated high-spin ground states arising via a double exchange mechanism. The broader impacts of this research include a legacy of synthetic techniques, the creation of new materials of potential technological importance, and the education and training of postdoctoral, graduate, and undergraduate students in the synthesis and characterization of inorganic materials. As a related educational activity, the PI will take the lead in creating a materials chemistry major within the Dept. of Chemistry at UC Berkeley.