Design, Synthesis And Magnetic Properties Of Magnetically Bistable Supramolecular Aggregates

A large amount of magnetically bistable molecules or high dimensionalframeworks have been reported with the gradual prosperity in the field ofmolecular magnetism. However, the studies focused on elucidating the relationsbetween the local magnetic behavior of single ions and the global properties ofpolynuclear complexes are still limited.A possible route is to construct the supramolecular aggregates withdifferent coupling strengths based on mononuclear bistable complexes, and thedistinctions between their magnetic behaviors will shed light on the interactionsbetween single ion anisotropies, or the mechanism of synergy effect in the SCOcomplexes. Moreover, the coordination spheres of mononuclear complexes insupramolecular aggregates would deviate from those of isolated species, henceproviding opportunities for further theoretical study. Based on theseconsiderations, the main results of this thesis are outlined as follows:1. A series of tridentate ligands and corresponding bi-tridentateligands were synthesized. Four mononuclear complexes and theirsupramolecular aggregates were obtained, and were characterized by X-raysingle crystal diffraction.2. Two cobalt complexes (complex1and3) were demonstrated toexhibit thermal SCO behavior. Complex3is by far the highest nuclearitycobalt cluster exhibiting spin transition process.3. By changing the substituent group from Br to CH3, the Co2+ionswere oxidized to Co3+ions spontaneously in the air. This phenomenon isascribed to the weak electronic donating effect of methyl group, asconfirmed by DFT calculations.4. Two mononuclear dysprosium complexes with similar coordinationenvironments were obtained, and the SIM behaviors were observed. Theslow magnetic relaxations were originated from molecule nature, as furthercorroborated by magnetic dilution measurements. 5. Two2×2metallogrid-type dysprosium complexes were afforded, and theirfield-induced SMM behaviors were investigated. Considering the separation of Dy3+ions, the slow relaxations should be assigned to single-ion behaviors. Through thecomparison between mononuclear and tetranuclear Dy3+complexes, we get to theconclusion that the deviation from bi-augmented trigonal prism coordinationgeometry leads the enhancement in single ion anisotropy of Dy3+ion.