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 Dy^III-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}_<i>n</i> (<b>1</b>) and [Dy₂(FDA)₃(DMF)₂(CH₃OH)]_<i>n</i> (<b>2</b>) show similar three-dimensional structures, but the coordination geometries around the dysprosium­(III) ions in <b>1</b> and <b>2</b> exhibit different deviations from ideal square antiprism (<i>D</i>_4<i>d</i> 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 <b>1</b> and <b>2</b> can be obtained from alternating-current susceptibility measurements by applying an external 2000 Oe direct-current field. MOF <b>2</b> possesses a less distorted <i>D</i>_4<i>d</i> coordination sphere and gives a higher effective energy barrier (<i>U</i>_eff) than that of MOF <b>1</b>. Their diamagnetic Y^III-diluted samples <b>1@Y</b> and <b>2@Y</b> exhibit similar relationships between the geometries and <i>U</i>_eff values, demonstrating that the magnetization relaxation is mainly from the symmetry-related single-ion behavior