Constraining and Tuning the Coordination Geometry of a Lanthanide Ion in Metal–Organic Frameworks: Approach toward a Single-Molecule Magnet

It
is available to constrain and tune the coordination geometries around
lanthanide ions in metal–organic frameworks (MOFs) for the
study of single-molecule-magnet (SMM) behavior. A series of DyIII-MOFs are synthesized via a solvothermal method by using
furan-2,5-dicarboxylic acid (H2FDA) as the ligand. {[Dy2(FDA)3(DMF)2]·1.5DMF}n (1) and [Dy2(FDA)3(DMF)2(CH3OH)]n (2) show similar three-dimensional structures, but
the coordination geometries around the dysprosium­(III) ions in 1 and 2 exhibit different deviations from ideal
square antiprism (D4d symmetry) because of the coordinated solvent molecules. Slow relaxation
of the magnetization can be observed for both complexes, indicative
of SMM behavior. The effective energy barriers for 1 and 2 can be obtained from alternating-current susceptibility
measurements by applying an external 2000 Oe direct-current field.
MOF 2 possesses a less distorted D4d coordination sphere and gives a higher
effective energy barrier (Ueff) than that
of MOF 1. Their diamagnetic YIII-diluted samples 1@Y and 2@Y exhibit similar relationships between
the geometries and Ueff values, demonstrating
that the magnetization relaxation is mainly from the symmetry-related
single-ion behavior.