Modulating the Architectures of Cobalt Metal-Organic Frameworks to Fine-tune Slow Magnetic Relaxation Behaviors

By utilizing two similar tetrapyridine ligands, tetrakis(4-pyridyloxymethylene)methane (L1) and tetrakis(3-pyridyloxymethylene)methane (L2), four distinct metal-organic frameworks (MOFs), with formulas [Co(NCS)(2)(L1)]center dot CH3OH (HUST-13, HUST = Huazhong University of Science and Technology), [Co(NCS)(2)(L1)] (HUST-14), [Co(NCS)(2)(L2)]center dot 2(CH3OH) (HUST-15), and [Co(NCS)(2)(L2)] (HUST-16), have been successfully constructed by adjusting the reaction solvents. After structural characterization, four Co-MOFs exhibit versatile topological structures and a single cobalt node with octahedron configuration. The synergistic effect between the steric configuration of ligands and the structural director of solvent molecules must be responsible for the generation of the distinct topological structures. Magnetic studies reveal the presentation of different slow magnetic relaxation phenomena in these Co-MOFs, which should be ascribed to the different orientations of the magnetic anisotropic axis of cobalt ions in the corresponding frameworks. The related results adequately illustrate the feasibility of the construction strategy for single ion magnet (SIM) MOFs and inspire other research strategies for the development of molecular magnets.