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

Abstract

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}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 Y(III)-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.