Single molecule magnets (SMMs) are discrete molecules featuring magnetic anisotropy of purely molecular origin. In being the smallest modifiable magnetic unit, there has been significant interest in utilizing SMMs as the functional unit in the next generation of data storage and quantum processing devices. The interaction of multiple magnetically anisotropic lanthanide ions within a single molecule can result in increased magnetic moments and improved SMM properties compared to related mononuclear lanthanide SMMs. To this end, the controlled design of multi-nuclear lanthanide compounds poses a synthetic challenge due to the propensity of the large, Lewis acidic, lanthanide ions to engage in non-directional, ionic bonding interactions and to adopt high coordination numbers. Herein, we show that a family of organometallic Ln-[1]ferrocenophane SMMs, [LnFc₃Li₂(THF)₂]^- (1) (Fc = 1,1'-diferrocenyl), can be used as molecular building blocks for the non-serendipitous design of linear homo- and hetero-nuclear Ln₃-[1]ferrocenophane compounds of the type, [Ln₃Fc₆Li₂(THF)₂]^- and [LnFc₃Li₂(Ln'(COT))₂]^- (COT^2- = cyclooctatetraide), respectively. Compounds 2 and 3 feature unusually strong ferromagnetic coupling interactions and/or an increase in symmetry of the {LnFc₃} unit resulting in significantly enhanced SMM behavior for 2 and 3 compared to the mononuclear parent compounds, [LnFc₃Li₂(THF)₂]^-.

Jeffrey Rinehart

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