A Paramagnetic Compass Based on Lanthanide Metal-Organic Framework

Macroscopic compass-like magnetic alignment at low magnetic fields is natural for ferromagnetic materials but is seldomly observed in paramagnetic materials. Herein, we report a paramagnetic compass that magnetically aligns under & SIM;mT fields based on the single-crystalline framework constructed by lanthanide ions and organic ligands (Ln-MOF). The magnetic alignment is attributed to the Ln-MOF's strong macroscopic anisotropy, where the highly-ordered structure allows the Ln-ions' molecular anisotropy to be summed according to the crystal symmetry. In tetragonal Ln-MOFs, the alignment is either parallel or perpendicular to the field depending on the easiest axis of the molecular anisotropy. Reversible switching between the two alignments is realized upon the removal and re-adsorption of solvent molecules filled in the framework. When the crystal symmetry is lowered in monoclinic Ln-MOFs, the alignments become even inclined (47 & DEG;-66 & DEG;) to the field. These fascinating properties of Ln-MOFs would encourage further explorations of framework materials containing paramagnetic centers.

Automated summary

In this study, a single-crystalline framework material (Ln-MOF) is reported, which exhibits compass-like magnetic alignment under low magnetic fields. This magnetic alignment is attributed to the strong macroscopic anisotropy of Ln-MOF, where the highly-ordered structure allows the sum of molecular anisotropy of Ln-ions according to crystal symmetry. In tetragonal Ln-MOFs, the alignment can be either parallel or perpendicular to the field, depending on the easiest axis of molecular anisotropy. Reversible switching between the two alignments is realized by removing and re-adsorbing solvent molecules in the framework. When the crystal symmetry is lowered in monoclinic Ln-MOFs, the alignments become even inclined (47°-66°) to the field. These fascinating properties of Ln-MOFs would encourage further explorations of framework materials containing paramagnetic centers.