Due to the large intrinsic magnetic anisotropy of the lanthanide ions, rare-earth metal systems, and in particular dysprosium (Dy) based materials, have sparked increasing interest in the area of molecular magnetism. [1] In a molecular complex, when such a unique property is combined with a high-spin ground state (S), slow relaxation of the magnetization can be obtained as seen for single-molecule magnets (SMMs). [2] Although, a number of mixed transition-metal/ lanthanide SMMs have been reported, [3] pure lanthanide SMMs are relatively scarce. [1b, 4] The latter molecules are rare owing to the difficulty in promoting magnetic interactions in these systems. These interactions are attained by the overlap of bridging ligand orbitals with the 4f orbitals of the lanthanide ions. Thus, ligand design is one of the key components for achieving such interactions in pure lanthanide-based systems.
To induce significant magnetic interaction between the lanthanide ions and synthesize high-energy-barrier SMMs, we have been investigating the use of (2-hydroxy-3-methoxyphenyl)methylene (isonicotino)hydrazine (H 2 hmi) as a rigid chelate in lanthanide chemistry. Such a linear ligand provides O,N,O,O-based multichelating sites that are especially favorable for lanthanide ion complex formation. [5,6] They can form dinuclear systems using the bridging phenoxide oxygen atom, and the pyridine group promotes the formation of extended networks that can control the organization of the SMM units in the three-dimensional structure. Herein we report the use of the H 2 hmi ligand to design materials based on ferromagnetically coupled dinuclear dysprosium(III) SMMs with large relaxation barriers.